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Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity

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  Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity Philipp Zabel <p.zabel@pengutronix.de> - 2015-11-25 18:30 +0100
    Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity Manfred Schlaegl <manfred.schlaegl@gmx.at> - 2015-11-26 15:30 +0100
      Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity Tomi Valkeinen <tomi.valkeinen@ti.com> - 2015-11-27 08:40 +0100
        Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity Philipp Zabel <p.zabel@pengutronix.de> - 2015-11-30 22:10 +0100

#1277635 — Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity

Am Mittwoch, den 15.07.2015, 17:50 +0200 schrieb Manfred Schlaegl:
> To get full support for parallel and LVDS displays with drm:
> Add representation for clock and data enable polarity in drm_display_mode
> flags (similar to HSYNC/VSYNC polarity) and update conversion functions
> from/to videomode accordingly.
> 
> This is especially important for embedded devices where parallel(RGB) and
> LVDS displays are still widely used and drm already plays an important
> role.
> 
> Tested on Freescale i.MX53(parallel) and i.MX6(LVDS).
> 
> Background:
> There was the ability to set polarity of clock and data enable signals
> in devicetree(display-timing), struct display_timing and struct videomode,
> but there was no representation for this in struct drm_display_mode.
> Example on Freescale i.MX53/i.MX6 SoC's:
>  * A parallel display using different clock polarity is set up using
>    display-timing in devicetree
>  * ipuv3 parallel outputs clock with wrong polarity
> 
> Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at>

Any comments on whether data enable and pixel clock polarity flags can
be added to the visible DRM_MODE_FLAGs, and if not, where else this
information should be kept? struct drm_display_info?

This patch and the following IPUv3 patch are useful and necessary for
quite some panels connected to i.MX SoCs, but adding DRM_MODE_FLAGs is
somewhat out of my jurisdiction.

best regards
Philipp

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#1278257

On 2015-11-25 18:22, Philipp Zabel wrote:
> Am Mittwoch, den 15.07.2015, 17:50 +0200 schrieb Manfred Schlaegl:
>> To get full support for parallel and LVDS displays with drm:
>> Add representation for clock and data enable polarity in drm_display_mode
>> flags (similar to HSYNC/VSYNC polarity) and update conversion functions
>> from/to videomode accordingly.
>>
>> This is especially important for embedded devices where parallel(RGB) and
>> LVDS displays are still widely used and drm already plays an important
>> role.
>>
>> Tested on Freescale i.MX53(parallel) and i.MX6(LVDS).
>>
>> Background:
>> There was the ability to set polarity of clock and data enable signals
>> in devicetree(display-timing), struct display_timing and struct videomode,
>> but there was no representation for this in struct drm_display_mode.
>> Example on Freescale i.MX53/i.MX6 SoC's:
>>  * A parallel display using different clock polarity is set up using
>>    display-timing in devicetree
>>  * ipuv3 parallel outputs clock with wrong polarity
>>
>> Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at>
> 
> Any comments on whether data enable and pixel clock polarity flags can
> be added to the visible DRM_MODE_FLAGs, and if not, where else this
> information should be kept? struct drm_display_info?
> 
> This patch and the following IPUv3 patch are useful and necessary for
> quite some panels connected to i.MX SoCs, but adding DRM_MODE_FLAGs is
> somewhat out of my jurisdiction.
> 
> best regards
> Philipp
> 

Good to see that this discussion is triggered.

State of the sent patches respective to git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git (78c4a49)
 * [RFC PATCH 1/2] drm: add support for for clk and de polarity
   * applies unmodified
 * [RFC PATCH 2/2] gpu: ipu-v3: use clock and de polarity from videomode
   * does not apply -> but this can be fixed with corrections of line offsets (using patch)
From a code review I think the modifications must work, but I did no testing on kernel versions newer than 4.1.13.
On demand, I can redo tests on some of our i.MX53 (parallel) and i.MX6 (lvds) boards and send actual patches.

best regards,
Manfred

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#1278576

[Multipart message — attachments visible in raw view] — view raw

On 26/11/15 16:20, Manfred Schlaegl wrote:
> On 2015-11-25 18:22, Philipp Zabel wrote:
>> Am Mittwoch, den 15.07.2015, 17:50 +0200 schrieb Manfred Schlaegl:
>>> To get full support for parallel and LVDS displays with drm:
>>> Add representation for clock and data enable polarity in drm_display_mode
>>> flags (similar to HSYNC/VSYNC polarity) and update conversion functions
>>> from/to videomode accordingly.
>>>
>>> This is especially important for embedded devices where parallel(RGB) and
>>> LVDS displays are still widely used and drm already plays an important
>>> role.
>>>
>>> Tested on Freescale i.MX53(parallel) and i.MX6(LVDS).
>>>
>>> Background:
>>> There was the ability to set polarity of clock and data enable signals
>>> in devicetree(display-timing), struct display_timing and struct videomode,
>>> but there was no representation for this in struct drm_display_mode.
>>> Example on Freescale i.MX53/i.MX6 SoC's:
>>>  * A parallel display using different clock polarity is set up using
>>>    display-timing in devicetree
>>>  * ipuv3 parallel outputs clock with wrong polarity
>>>
>>> Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at>
>>
>> Any comments on whether data enable and pixel clock polarity flags can
>> be added to the visible DRM_MODE_FLAGs, and if not, where else this
>> information should be kept? struct drm_display_info?
>>
>> This patch and the following IPUv3 patch are useful and necessary for
>> quite some panels connected to i.MX SoCs, but adding DRM_MODE_FLAGs is
>> somewhat out of my jurisdiction.
>>
>> best regards
>> Philipp
>>
> 
> Good to see that this discussion is triggered.

I seem to have missed this one. This is important for omapdrm also.
We've had similar patch in TI's linux for a while, but I have never had
time to start upstreaming it.

Two comments:

The "pixclock polarity" could be explained a bit, as it's not really
about polarity. This was discussed when the display-timings stuff was
worked on, and display-timings.txt explains what the "pixelclk-active"
property means.

So here I think you could maybe have a comment pointing to
display-timings.txt, or perhaps a short comment about what the flag is.
Or if you come up with a great name for the define, that's good too =).

The other comment is not about this patch as such, but similar flags
that OMAP has, and possibly some other platforms too:

1) sync signals driven on rising or falling edge of pixel clock
2) hsync and vsync happen at the same time or hsync happens first,
followed by vsync

Any other platforms have similar features?

 Tomi

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#1280284

Am Freitag, den 27.11.2015, 09:37 +0200 schrieb Tomi Valkeinen:
> On 26/11/15 16:20, Manfred Schlaegl wrote:
> > Good to see that this discussion is triggered.
> 
> I seem to have missed this one. This is important for omapdrm also.
> We've had similar patch in TI's linux for a while, but I have never had
> time to start upstreaming it.
> 
> Two comments:
> 
> The "pixclock polarity" could be explained a bit, as it's not really
> about polarity. This was discussed when the display-timings stuff was
> worked on, and display-timings.txt explains what the "pixelclk-active"
> property means.

Yes, the relevant part of this setting is whether the panel will sample
the data bus on the falling or rising edge of the pixel clock signal.
The display interface has guarantee that the data bus is stable around
that time.

> So here I think you could maybe have a comment pointing to
> display-timings.txt, or perhaps a short comment about what the flag is.
> Or if you come up with a great name for the define, that's good too =).

We have the choice of describing the flag from point of view of the
display controller (as the DISPLAY_FLAGS do), from point of view of the
panel, or using a somewhat neutral description like in the device tree.
Which choice I'd prefer depends on whether the flags go into
drm_display_mode / drm_mode_modeinfo or in drm_display_info.

In any case, I think that it'd be better to talk about driving or
sampling data on rising or falling edges instead of clock polarity.

> The other comment is not about this patch as such, but similar flags
> that OMAP has, and possibly some other platforms too:
> 
> 1) sync signals driven on rising or falling edge of pixel clock
> 2) hsync and vsync happen at the same time or hsync happens first,
> followed by vsync
> 
> Any other platforms have similar features?

The i.MX6 display interface consists of a number of rather freely
configurable signal generators, so all of this should be possible to do.

regards
Philipp

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