Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1570596 > unrolled thread

[PATCH v2] drm/color: Document CTM eqations

Back to article view | Back to linux.kernel

Contents

  [PATCH v2] drm/color: Document CTM eqations Brian Starkey <brian.starkey@arm.com> - 2017-01-31 11:50 +0100
    Re: [PATCH v2] drm/color: Document CTM eqations Jani Nikula <jani.nikula@linux.intel.com> - 2017-01-31 12:40 +0100
      Re: [PATCH v2] drm/color: Document CTM eqations Brian Starkey <brian.starkey@arm.com> - 2017-01-31 13:10 +0100
        Re: [PATCH v2] drm/color: Document CTM eqations Jani Nikula <jani.nikula@linux.intel.com> - 2017-01-31 13:40 +0100
    Re: [PATCH v2] drm/color: Document CTM eqations Ville Syrjälä <ville.syrjala@linux.intel.com> - 2017-01-31 16:20 +0100
      Re: [PATCH v2] drm/color: Document CTM eqations Brian Starkey <brian.starkey@arm.com> - 2017-01-31 16:50 +0100
        Re: [PATCH v2] drm/color: Document CTM eqations Daniel Vetter <daniel.vetter@ffwll.ch> - 2017-01-31 18:50 +0100
        Re: [PATCH v2] drm/color: Document CTM eqations Ville Syrjälä <ville.syrjala@linux.intel.com> - 2017-01-31 19:10 +0100

#1570596 — [PATCH v2] drm/color: Document CTM eqations

Explicitly state the expected CTM equations in the kerneldoc for the CTM
property, and the form of the matrix on struct drm_color_ctm.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Brian Starkey <brian.starkey@arm.com>
---
 drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
 include/uapi/drm/drm_mode.h      |    8 +++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 789b4c65cd69..7573ca4b6ea6 100644
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -62,6 +62,19 @@
  *	unit/pass-thru matrix should be used. This is generally the driver
  *	boot-up state too.
  *
+ *	The output vector is related to the input vector as below:
+ *
+ *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
+ *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
+ *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
+ *
+ *	The component order in the input/output vectors is assumed to be
+ *	{ R, G, B }.
+ *
+ *	The color-space of the input vector must not be confused with the
+ *	color-space implied by a framebuffer pixel format, which may be the same
+ *	or different.
+ *
  * “GAMMA_LUT”:
  *	Blob property to set the gamma lookup table (LUT) mapping pixel data
  *	after the transformation matrix to data sent to the connector. The
diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index ce7efe2e8a5e..3401637caf8e 100644
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
 };
 
 struct drm_color_ctm {
-	/* Conversion matrix in S31.32 format. */
+	/*
+	 * Conversion matrix in S31.32 format, in row-major form:
+	 *
+	 * | matrix[0] matrix[1] matrix[2] |
+	 * | matrix[3] matrix[4] matrix[5] |
+	 * | matrix[6] matrix[7] matrix[8] |
+	 */
 	__s64 matrix[9];
 };
 
-- 
1.7.9.5

[toc] | [next] | [standalone]

#1570628

On Tue, 31 Jan 2017, Brian Starkey <brian.starkey@arm.com> wrote:
> Explicitly state the expected CTM equations in the kerneldoc for the CTM
> property, and the form of the matrix on struct drm_color_ctm.
>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> ---
>  drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
>  include/uapi/drm/drm_mode.h      |    8 +++++++-
>  2 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> index 789b4c65cd69..7573ca4b6ea6 100644
> --- a/drivers/gpu/drm/drm_color_mgmt.c
> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> @@ -62,6 +62,19 @@
>   *	unit/pass-thru matrix should be used. This is generally the driver
>   *	boot-up state too.
>   *
> + *	The output vector is related to the input vector as below:
> + *
> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``

Would that not work better with a preformatted block? Replace the colon
in the preceding paragraph with the double colon ::, and indent the
block.

> + *
> + *	The component order in the input/output vectors is assumed to be
> + *	{ R, G, B }.
> + *
> + *	The color-space of the input vector must not be confused with the
> + *	color-space implied by a framebuffer pixel format, which may be the same
> + *	or different.
> + *
>   * “GAMMA_LUT”:
>   *	Blob property to set the gamma lookup table (LUT) mapping pixel data
>   *	after the transformation matrix to data sent to the connector. The
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index ce7efe2e8a5e..3401637caf8e 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
>  };
>  
>  struct drm_color_ctm {
> -	/* Conversion matrix in S31.32 format. */
> +	/*
> +	 * Conversion matrix in S31.32 format, in row-major form:
> +	 *
> +	 * | matrix[0] matrix[1] matrix[2] |
> +	 * | matrix[3] matrix[4] matrix[5] |
> +	 * | matrix[6] matrix[7] matrix[8] |
> +	 */

Same here.

>  	__s64 matrix[9];
>  };

-- 
Jani Nikula, Intel Open Source Technology Center

[toc] | [prev] | [next] | [standalone]

#1570653

Hi Jani,

On Tue, Jan 31, 2017 at 01:30:41PM +0200, Jani Nikula wrote:
>On Tue, 31 Jan 2017, Brian Starkey <brian.starkey@arm.com> wrote:
>> Explicitly state the expected CTM equations in the kerneldoc for the CTM
>> property, and the form of the matrix on struct drm_color_ctm.
>>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>> ---
>>  drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
>>  include/uapi/drm/drm_mode.h      |    8 +++++++-
>>  2 files changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
>> index 789b4c65cd69..7573ca4b6ea6 100644
>> --- a/drivers/gpu/drm/drm_color_mgmt.c
>> +++ b/drivers/gpu/drm/drm_color_mgmt.c
>> @@ -62,6 +62,19 @@
>>   *	unit/pass-thru matrix should be used. This is generally the driver
>>   *	boot-up state too.
>>   *
>> + *	The output vector is related to the input vector as below:
>> + *
>> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
>> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
>> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
>
>Would that not work better with a preformatted block? Replace the colon
>in the preceding paragraph with the double colon ::, and indent the
>block.
>

Ah thanks for the tip, I couldn't get it to work but it looks like my
syntax was a bit off. I'll resend with that change.

>> + *
>> + *	The component order in the input/output vectors is assumed to be
>> + *	{ R, G, B }.
>> + *
>> + *	The color-space of the input vector must not be confused with the
>> + *	color-space implied by a framebuffer pixel format, which may be the same
>> + *	or different.
>> + *
>>   * “GAMMA_LUT”:
>>   *	Blob property to set the gamma lookup table (LUT) mapping pixel data
>>   *	after the transformation matrix to data sent to the connector. The
>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>> index ce7efe2e8a5e..3401637caf8e 100644
>> --- a/include/uapi/drm/drm_mode.h
>> +++ b/include/uapi/drm/drm_mode.h
>> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
>>  };
>>
>>  struct drm_color_ctm {
>> -	/* Conversion matrix in S31.32 format. */
>> +	/*
>> +	 * Conversion matrix in S31.32 format, in row-major form:
>> +	 *
>> +	 * | matrix[0] matrix[1] matrix[2] |
>> +	 * | matrix[3] matrix[4] matrix[5] |
>> +	 * | matrix[6] matrix[7] matrix[8] |
>> +	 */
>
>Same here.

This comment isn't actually kerneldoc, so I guess not rst either.
I can include the markup if you like, but the |s here were to indicate
it's a matrix rather than for rst.

Cheers,
-Brian

>
>>  	__s64 matrix[9];
>>  };
>
>-- 
>Jani Nikula, Intel Open Source Technology Center

[toc] | [prev] | [next] | [standalone]

#1570685

On Tue, 31 Jan 2017, Brian Starkey <brian.starkey@arm.com> wrote:
> Hi Jani,
>
> On Tue, Jan 31, 2017 at 01:30:41PM +0200, Jani Nikula wrote:
>>On Tue, 31 Jan 2017, Brian Starkey <brian.starkey@arm.com> wrote:
>>> Explicitly state the expected CTM equations in the kerneldoc for the CTM
>>> property, and the form of the matrix on struct drm_color_ctm.
>>>
>>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
>>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>>> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>>> ---
>>>  drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
>>>  include/uapi/drm/drm_mode.h      |    8 +++++++-
>>>  2 files changed, 20 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
>>> index 789b4c65cd69..7573ca4b6ea6 100644
>>> --- a/drivers/gpu/drm/drm_color_mgmt.c
>>> +++ b/drivers/gpu/drm/drm_color_mgmt.c
>>> @@ -62,6 +62,19 @@
>>>   *	unit/pass-thru matrix should be used. This is generally the driver
>>>   *	boot-up state too.
>>>   *
>>> + *	The output vector is related to the input vector as below:
>>> + *
>>> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
>>> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
>>> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
>>
>>Would that not work better with a preformatted block? Replace the colon
>>in the preceding paragraph with the double colon ::, and indent the
>>block.
>>
>
> Ah thanks for the tip, I couldn't get it to work but it looks like my
> syntax was a bit off. I'll resend with that change.
>
>>> + *
>>> + *	The component order in the input/output vectors is assumed to be
>>> + *	{ R, G, B }.
>>> + *
>>> + *	The color-space of the input vector must not be confused with the
>>> + *	color-space implied by a framebuffer pixel format, which may be the same
>>> + *	or different.
>>> + *
>>>   * “GAMMA_LUT”:
>>>   *	Blob property to set the gamma lookup table (LUT) mapping pixel data
>>>   *	after the transformation matrix to data sent to the connector. The
>>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>>> index ce7efe2e8a5e..3401637caf8e 100644
>>> --- a/include/uapi/drm/drm_mode.h
>>> +++ b/include/uapi/drm/drm_mode.h
>>> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
>>>  };
>>>
>>>  struct drm_color_ctm {
>>> -	/* Conversion matrix in S31.32 format. */
>>> +	/*
>>> +	 * Conversion matrix in S31.32 format, in row-major form:
>>> +	 *
>>> +	 * | matrix[0] matrix[1] matrix[2] |
>>> +	 * | matrix[3] matrix[4] matrix[5] |
>>> +	 * | matrix[6] matrix[7] matrix[8] |
>>> +	 */
>>
>>Same here.
>
> This comment isn't actually kerneldoc, so I guess not rst either.
> I can include the markup if you like, but the |s here were to indicate
> it's a matrix rather than for rst.

Oh, right. Up to you.

>
> Cheers,
> -Brian
>
>>
>>>  	__s64 matrix[9];
>>>  };
>>
>>-- 
>>Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center

[toc] | [prev] | [next] | [standalone]

#1570817

On Tue, Jan 31, 2017 at 10:48:34AM +0000, Brian Starkey wrote:
> Explicitly state the expected CTM equations in the kerneldoc for the CTM
> property, and the form of the matrix on struct drm_color_ctm.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> ---
>  drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
>  include/uapi/drm/drm_mode.h      |    8 +++++++-
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> index 789b4c65cd69..7573ca4b6ea6 100644
> --- a/drivers/gpu/drm/drm_color_mgmt.c
> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> @@ -62,6 +62,19 @@
>   *	unit/pass-thru matrix should be used. This is generally the driver
>   *	boot-up state too.
>   *
> + *	The output vector is related to the input vector as below:
> + *
> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
> + *
> + *	The component order in the input/output vectors is assumed to be
> + *	{ R, G, B }.
> + *
> + *	The color-space of the input vector must not be confused with the
> + *	color-space implied by a framebuffer pixel format, which may be the same
> + *	or different.
> + *
>   * “GAMMA_LUT”:
>   *	Blob property to set the gamma lookup table (LUT) mapping pixel data
>   *	after the transformation matrix to data sent to the connector. The
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index ce7efe2e8a5e..3401637caf8e 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
>  };
>  
>  struct drm_color_ctm {
> -	/* Conversion matrix in S31.32 format. */
> +	/*
> +	 * Conversion matrix in S31.32 format, in row-major form:

s32.32 is how I'd state that (to match the regular s32 and whatnot
types).

> +	 *
> +	 * | matrix[0] matrix[1] matrix[2] |
> +	 * | matrix[3] matrix[4] matrix[5] |
> +	 * | matrix[6] matrix[7] matrix[8] |
> +	 */
>  	__s64 matrix[9];
>  };
>  
> -- 
> 1.7.9.5

-- 
Ville Syrjälä
Intel OTC

[toc] | [prev] | [next] | [standalone]

#1570835

Hi Ville,

On Tue, Jan 31, 2017 at 05:18:28PM +0200, Ville Syrjälä wrote:
>On Tue, Jan 31, 2017 at 10:48:34AM +0000, Brian Starkey wrote:
>> Explicitly state the expected CTM equations in the kerneldoc for the CTM
>> property, and the form of the matrix on struct drm_color_ctm.
>>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
>> ---
>>  drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
>>  include/uapi/drm/drm_mode.h      |    8 +++++++-
>>  2 files changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
>> index 789b4c65cd69..7573ca4b6ea6 100644
>> --- a/drivers/gpu/drm/drm_color_mgmt.c
>> +++ b/drivers/gpu/drm/drm_color_mgmt.c
>> @@ -62,6 +62,19 @@
>>   *	unit/pass-thru matrix should be used. This is generally the driver
>>   *	boot-up state too.
>>   *
>> + *	The output vector is related to the input vector as below:
>> + *
>> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
>> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
>> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
>> + *
>> + *	The component order in the input/output vectors is assumed to be
>> + *	{ R, G, B }.
>> + *
>> + *	The color-space of the input vector must not be confused with the
>> + *	color-space implied by a framebuffer pixel format, which may be the same
>> + *	or different.
>> + *
>>   * “GAMMA_LUT”:
>>   *	Blob property to set the gamma lookup table (LUT) mapping pixel data
>>   *	after the transformation matrix to data sent to the connector. The
>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>> index ce7efe2e8a5e..3401637caf8e 100644
>> --- a/include/uapi/drm/drm_mode.h
>> +++ b/include/uapi/drm/drm_mode.h
>> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
>>  };
>>
>>  struct drm_color_ctm {
>> -	/* Conversion matrix in S31.32 format. */
>> +	/*
>> +	 * Conversion matrix in S31.32 format, in row-major form:
>
>s32.32 is how I'd state that (to match the regular s32 and whatnot
>types).
>

Can you explain a bit more what exactly you mean by s32.32? e.g. what
would be the bitfield representing the most negative number?

I understand the S31.32 here as a sign + magnitude format (which makes
it rather odd to store it in a signed variable, but never mind). This
also appears to be what igt does in set_ctm() in kms_pipe_color.c:

	for (i = 0; i < ARRAY_SIZE(ctm.matrix); i++) {
		if (coefficients[i] < 0) {
			ctm.matrix[i] =
				(int64_t) (-coefficients[i] * ((int64_t) 1L << 32));
			ctm.matrix[i] |= 1ULL << 63;
		} else
			ctm.matrix[i] =
				(int64_t) (coefficients[i] * ((int64_t) 1L << 32));
	}

If that's what you meant as well, then I don't think s32.32 is a good
way to describe it, because the integer part has only 31 bits
available.

If you meant a regular two's-complement fixed-point number, where the
most negative number would be 0x10000000.00000000, then yeah that's
what I thought it meant too originally. Clarifying the docs here
sounds like a great plan.

I guess the igt implementation means that it's a sign + magnitude
number, and the fact that it's stored in an s64 is a bizarre quirk
that we just live with.

Cheers,
Brian

>> +	 *
>> +	 * | matrix[0] matrix[1] matrix[2] |
>> +	 * | matrix[3] matrix[4] matrix[5] |
>> +	 * | matrix[6] matrix[7] matrix[8] |
>> +	 */
>>  	__s64 matrix[9];
>>  };
>>
>> --
>> 1.7.9.5
>
>-- 
>Ville Syrjälä
>Intel OTC

[toc] | [prev] | [next] | [standalone]

#1570936

On Tue, Jan 31, 2017 at 6:22 PM, Ville Syrjälä
<ville.syrjala@linux.intel.com> wrote:
>> >> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>> >> index ce7efe2e8a5e..3401637caf8e 100644
>> >> --- a/include/uapi/drm/drm_mode.h
>> >> +++ b/include/uapi/drm/drm_mode.h
>> >> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
>> >>  };
>> >>
>> >>  struct drm_color_ctm {
>> >> -  /* Conversion matrix in S31.32 format. */
>> >> +  /*
>> >> +   * Conversion matrix in S31.32 format, in row-major form:
>> >
>> >s32.32 is how I'd state that (to match the regular s32 and whatnot
>> >types).
>> >
>>
>> Can you explain a bit more what exactly you mean by s32.32? e.g. what
>> would be the bitfield representing the most negative number?
>>
>> I understand the S31.32 here as a sign + magnitude format (which makes
>> it rather odd to store it in a signed variable, but never mind). This
>> also appears to be what igt does in set_ctm() in kms_pipe_color.c:
>>
>>       for (i = 0; i < ARRAY_SIZE(ctm.matrix); i++) {
>>               if (coefficients[i] < 0) {
>>                       ctm.matrix[i] =
>>                               (int64_t) (-coefficients[i] * ((int64_t) 1L << 32));
>>                       ctm.matrix[i] |= 1ULL << 63;
>>               } else
>>                       ctm.matrix[i] =
>>                               (int64_t) (coefficients[i] * ((int64_t) 1L << 32));
>>       }
>>
>> If that's what you meant as well, then I don't think s32.32 is a good
>> way to describe it, because the integer part has only 31 bits
>> available.
>>
>> If you meant a regular two's-complement fixed-point number, where the
>> most negative number would be 0x10000000.00000000, then yeah that's
>> what I thought it meant too originally. Clarifying the docs here
>> sounds like a great plan.
>>
>> I guess the igt implementation means that it's a sign + magnitude
>> number, and the fact that it's stored in an s64 is a bizarre quirk
>> that we just live with.
>
> Hmm. Two's complement is what I was thinking it is. Which shows that
> I never managed to read the code in any detail. Definitely needs to
> be documented properly.

That sounds supremely backwards. I guess we can't fix this anymore?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

[toc] | [prev] | [next] | [standalone]

#1570952

On Tue, Jan 31, 2017 at 03:39:29PM +0000, Brian Starkey wrote:
> Hi Ville,
> 
> On Tue, Jan 31, 2017 at 05:18:28PM +0200, Ville Syrjälä wrote:
> >On Tue, Jan 31, 2017 at 10:48:34AM +0000, Brian Starkey wrote:
> >> Explicitly state the expected CTM equations in the kerneldoc for the CTM
> >> property, and the form of the matrix on struct drm_color_ctm.
> >>
> >> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >> Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> >> Signed-off-by: Brian Starkey <brian.starkey@arm.com>
> >> ---
> >>  drivers/gpu/drm/drm_color_mgmt.c |   13 +++++++++++++
> >>  include/uapi/drm/drm_mode.h      |    8 +++++++-
> >>  2 files changed, 20 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
> >> index 789b4c65cd69..7573ca4b6ea6 100644
> >> --- a/drivers/gpu/drm/drm_color_mgmt.c
> >> +++ b/drivers/gpu/drm/drm_color_mgmt.c
> >> @@ -62,6 +62,19 @@
> >>   *	unit/pass-thru matrix should be used. This is generally the driver
> >>   *	boot-up state too.
> >>   *
> >> + *	The output vector is related to the input vector as below:
> >> + *
> >> + *	| ``out[0] = matrix[0] * in[0] + matrix[1] * in[1] + matrix[2] * in[2];``
> >> + *	| ``out[1] = matrix[3] * in[0] + matrix[4] * in[1] + matrix[5] * in[2];``
> >> + *	| ``out[2] = matrix[6] * in[0] + matrix[7] * in[1] + matrix[8] * in[2];``
> >> + *
> >> + *	The component order in the input/output vectors is assumed to be
> >> + *	{ R, G, B }.
> >> + *
> >> + *	The color-space of the input vector must not be confused with the
> >> + *	color-space implied by a framebuffer pixel format, which may be the same
> >> + *	or different.
> >> + *
> >>   * “GAMMA_LUT”:
> >>   *	Blob property to set the gamma lookup table (LUT) mapping pixel data
> >>   *	after the transformation matrix to data sent to the connector. The
> >> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> >> index ce7efe2e8a5e..3401637caf8e 100644
> >> --- a/include/uapi/drm/drm_mode.h
> >> +++ b/include/uapi/drm/drm_mode.h
> >> @@ -525,7 +525,13 @@ struct drm_mode_crtc_lut {
> >>  };
> >>
> >>  struct drm_color_ctm {
> >> -	/* Conversion matrix in S31.32 format. */
> >> +	/*
> >> +	 * Conversion matrix in S31.32 format, in row-major form:
> >
> >s32.32 is how I'd state that (to match the regular s32 and whatnot
> >types).
> >
> 
> Can you explain a bit more what exactly you mean by s32.32? e.g. what
> would be the bitfield representing the most negative number?
> 
> I understand the S31.32 here as a sign + magnitude format (which makes
> it rather odd to store it in a signed variable, but never mind). This
> also appears to be what igt does in set_ctm() in kms_pipe_color.c:
> 
> 	for (i = 0; i < ARRAY_SIZE(ctm.matrix); i++) {
> 		if (coefficients[i] < 0) {
> 			ctm.matrix[i] =
> 				(int64_t) (-coefficients[i] * ((int64_t) 1L << 32));
> 			ctm.matrix[i] |= 1ULL << 63;
> 		} else
> 			ctm.matrix[i] =
> 				(int64_t) (coefficients[i] * ((int64_t) 1L << 32));
> 	}
> 
> If that's what you meant as well, then I don't think s32.32 is a good
> way to describe it, because the integer part has only 31 bits
> available.
> 
> If you meant a regular two's-complement fixed-point number, where the
> most negative number would be 0x10000000.00000000, then yeah that's
> what I thought it meant too originally. Clarifying the docs here
> sounds like a great plan.
> 
> I guess the igt implementation means that it's a sign + magnitude
> number, and the fact that it's stored in an s64 is a bizarre quirk
> that we just live with.

Hmm. Two's complement is what I was thinking it is. Which shows that
I never managed to read the code in any detail. Definitely needs to
be documented properly.

-- 
Ville Syrjälä
Intel OTC

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web