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

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Message-ID: <20250321-adaptable-astonishing-adder-ceeb6f@houat>
Date: Fri, 21 Mar 2025 15:17:57 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
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

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.

Maxime

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