Re: [PATCH 3/8] drm/vc4: Use drm_mode_vrefresh() in DSI fixup, in case vrefresh is 0.

From	Andrzej Hajda <a.hajda@samsung.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/8] drm/vc4: Use drm_mode_vrefresh() in DSI fixup, in case vrefresh is 0.
Date	2017-06-29 11:30 +0200
Message-ID	<tXDVT-5Ni-7@gated-at.bofh.it> (permalink)
References	<tX4Ou-5bs-11@gated-at.bofh.it> <tXDVT-5Ni-9@gated-at.bofh.it> <tX4Y9-5uo-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On 27.06.2017 21:58, Eric Anholt wrote:
> I'm not sure what changed where I started getting vrefresh=0 from the
> mode to be fixed up.

It can be a case of low pixel_clock value, maybe it should be
investigated further, unless there is execution path with forgotten
mode->vrefresh =

drm_mode_vrefresh(mode)

>
> Signed-off-by: Eric Anholt <eric@anholt.net>
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 629d372633e6..fca4d7fd677e 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -866,7 +866,9 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder,
>  	adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
>  
>  	/* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
> -	adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * mode->vtotal);
> +	adjusted_mode->htotal = pixel_clock_hz / (drm_mode_vrefresh(mode) *
> +						  mode->vtotal);
> +

I am not sure but I guess division by zero is also possible here.
I do not know if you need to handle interlaced/dblscan/vscan modes, but
maybe it would be safer to calculate adjusted_htotal according to:

adjusted_mode->htotal = pixel_clock_hz * mode->htotal / (mode->clock * 1000)

or sth similar.


Regards
Andrzej

>  	adjusted_mode->hsync_end += adjusted_mode->htotal - mode->htotal;
>  	adjusted_mode->hsync_start += adjusted_mode->htotal - mode->htotal;
>

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH 3/8] drm/vc4: Use drm_mode_vrefresh() in DSI fixup, in case vrefresh is 0. Eric Anholt <eric@anholt.net> - 2017-06-27 22:10 +0200
  Re: [PATCH 3/8] drm/vc4: Use drm_mode_vrefresh() in DSI fixup,  in case vrefresh is 0. Andrzej Hajda <a.hajda@samsung.com> - 2017-06-29 11:30 +0200

csiph-web