linux-kernel - Re: [PATCH 03/18] drm/tidss: Add mode_fixup to adjust the clock based on HW

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Message-ID: <6ea0ee71-7cf6-4e96-aab0-6f4c72613bd1@ideasonboard.com>
Date: Wed, 2 Apr 2025 15:16:26 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Jyri Sarha <jyri.sarha@....fi>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 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>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 linux-phy@...ts.infradead.org, Francesco Dolcini <francesco@...cini.it>,
 Aradhya Bhatia <aradhya.bhatia@...ux.dev>, Devarsh Thakkar <devarsht@...com>
Subject: Re: [PATCH 03/18] drm/tidss: Add mode_fixup to adjust the clock based
 on HW

Hi,

On 21/03/2025 16:17, Maxime Ripard wrote:
> On Thu, Mar 20, 2025 at 05:59:58PM +0200, Tomi Valkeinen wrote:
>> At the moment the driver just sets the clock rate with clk_set_rate(),
>> and if the resulting rate is not the same as requested, prints a debug
>> print, but nothing else.
>>
>> Add mode_fixup(), in which the clk_round_rate() is used to get the
>> "rounded" rate, and set that to the adjusted_mode.
>>
>> In practice, with the current K3 SoCs, the display PLL is capable of
>> producing very exact clocks, so most likely the rounded rate is the same
>> as the original one.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
>> ---
>>   drivers/gpu/drm/tidss/tidss_crtc.c  | 22 ++++++++++++++++++++++
>>   drivers/gpu/drm/tidss/tidss_dispc.c |  6 ++++++
>>   drivers/gpu/drm/tidss/tidss_dispc.h |  2 ++
>>   3 files changed, 30 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/tidss/tidss_crtc.c b/drivers/gpu/drm/tidss/tidss_crtc.c
>> index 1604eca265ef..b3338dac25bc 100644
>> --- a/drivers/gpu/drm/tidss/tidss_crtc.c
>> +++ b/drivers/gpu/drm/tidss/tidss_crtc.c
>> @@ -309,7 +309,29 @@ 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)
>> +{
>> +	struct tidss_crtc *tcrtc = to_tidss_crtc(crtc);
>> +	struct drm_device *ddev = crtc->dev;
>> +	struct tidss_device *tidss = to_tidss(ddev);
>> +	long rate;
>> +
>> +	rate = dispc_vp_round_clk_rate(tidss->dispc, tcrtc->hw_videoport,
>> +				       adjusted_mode->clock * 1000);
>> +	if (rate < 0)
>> +		return false;
>> +
>> +	adjusted_mode->clock = rate / 1000;
>> +
>> +	drm_mode_set_crtcinfo(adjusted_mode, 0);
>> +
>> +	return true;
>> +}
> 
> mode_fixup is deprecated in favor of atomic_check. If you can't use it
> for some reason, it should be documented one way or another.

Ok. I didn't see a note about it being deprecated (just optional), so I 
went with fixup. Atomic check is called for every commit, and this 
should be only done before enabling a ctrc. I need to dig that 
"going-to-be-enabled" from the state.

  Tomi