linux-kernel - Re: [PATCH 1/7] drm/tidss: Add CRTC mode

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Message-ID: <ce332f8d-3a4f-4046-bde0-6e12c99ebb09@ti.com>
Date: Thu, 30 May 2024 15:09:42 +0530
From: Aradhya Bhatia <a-bhatia1@...com>
To: Maxime Ripard <mripard@...nel.org>
CC: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        Andrzej Hajda
	<andrzej.hajda@...el.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert
 Foss <rfoss@...nel.org>,
        Laurent Pinchart
	<Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej
 Skrabec <jernej.skrabec@...il.com>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Jyri Sarha <jyri.sarha@....fi>,
        Thomas
 Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Daniel
 Vetter <daniel@...ll.ch>,
        DRI Development List
	<dri-devel@...ts.freedesktop.org>,
        Linux Kernel List
	<linux-kernel@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>, Thierry
 Reding <treding@...dia.com>,
        Kieran Bingham
	<kieran.bingham+renesas@...asonboard.com>,
        Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>,
        Devarsh Thakkar <devarsht@...com>,
        Jayesh
 Choudhary <j-choudhary@...com>, Jai Luthra <j-luthra@...com>
Subject: Re: [PATCH 1/7] drm/tidss: Add CRTC mode_fixup

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@...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