Re: [PATCH 1/7] drm/tidss: Add CRTC mode_fixup

[Aradhya Bhatia <a-bhatia1@ti.com>]

Hi Maxime,

On 21/05/24 18:48, Maxime Ripard wrote:
> On Thu, May 16, 2024 at 04:33:40PM GMT, Aradhya Bhatia wrote:
>> Hi Maxime,
>>
>> Thank you for reviewing the patches.
>>
>> On 16/05/24 13:40, Maxime Ripard wrote:
>>> Hi,
>>>
>>> On Sat, May 11, 2024 at 09:00:45PM +0530, Aradhya Bhatia wrote:
>>>> Add support for mode_fixup for the tidss CRTC.
>>>>
>>>> Some bridges like the cdns-dsi consume the crtc_* timing parameters for
>>>> programming the blanking values. Allow for the normal timing parameters
>>>> to get copied to crtc_* timing params.
>>>>
>>>> Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
>>>> ---
>>>>  drivers/gpu/drm/tidss/tidss_crtc.c | 11 +++++++++++
>>>>  1 file changed, 11 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/tidss/tidss_crtc.c b/drivers/gpu/drm/tidss/tidss_crtc.c
>>>> index 94f8e3178df5..797ef53d9ad2 100644
>>>> --- a/drivers/gpu/drm/tidss/tidss_crtc.c
>>>> +++ b/drivers/gpu/drm/tidss/tidss_crtc.c
>>>> @@ -309,12 +309,23 @@ enum drm_mode_status tidss_crtc_mode_valid(struct drm_crtc *crtc,
>>>>  	return dispc_vp_mode_valid(tidss->dispc, tcrtc->hw_videoport, mode);
>>>>  }
>>>>  
>>>> +static
>>>> +bool tidss_crtc_mode_fixup(struct drm_crtc *crtc,
>>>> +			   const struct drm_display_mode *mode,
>>>> +			   struct drm_display_mode *adjusted_mode)
>>>> +{
>>>> +	drm_mode_set_crtcinfo(adjusted_mode, 0);
>>>> +
>>>> +	return true;
>>>> +}
>>>> +
>>>>  static const struct drm_crtc_helper_funcs tidss_crtc_helper_funcs = {
>>>>  	.atomic_check = tidss_crtc_atomic_check,
>>>>  	.atomic_flush = tidss_crtc_atomic_flush,
>>>>  	.atomic_enable = tidss_crtc_atomic_enable,
>>>>  	.atomic_disable = tidss_crtc_atomic_disable,
>>>>  
>>>> +	.mode_fixup = tidss_crtc_mode_fixup,
>>>>  	.mode_valid = tidss_crtc_mode_valid,
>>>>  };
>>>
>>> mode_fixup is deprecated for atomic drivers, so the solution must be
>>> different there.
>>>
>>> It's also not clear to me how it could change anything there:
>>> drm_mode_set_crtcinfo with no flags will make crtc_* field exactly
>>> identical to their !crtc counterparts.
>>>
>>
>> I checked the flag options. There isn't any flag required. The only
>> reason to add this call is because cdns-dsi strictly requires the crtc_*
>> fields to be populated during the bridge enable.
>>
>> Secondly, if mode_fixup is deprecated, I think the crtc_atomic_check
>> would be the next best place to add this call.
> 
> That would be better, yes, but we shouldn't even have to do that in the
> first place. AFAIK all the path that create a drm_display_mode will call
> drm_mode_set_crtcinfo on it to fill those fields. So if they are missing
> somewhere, that's what the actual bug is, not something we should work
> around of at the driver level.
> 

You are right. This patch isn't required at all. The fix around the
mode->crtc_clock usage in one place in the cdns-dsi driver makes this
patch unnecessary. The DRM core does duplicate the timing parameters at
a later stage for the cdns-dsi bridge_enable to consume.

Dropped this patch in v2. Thanks!

Regards
Aradhya