linux-kernel - Re: [PATCH v4 08/13] drm/stm: ltdc: handle lvds pixel clock

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Message-ID: <6bc77ea8-c664-45ff-886a-aefc79767253@foss.st.com>
Date: Fri, 22 Aug 2025 14:56:33 +0200
From: Yannick FERTRE <yannick.fertre@...s.st.com>
To: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        Philippe Cornu
	<philippe.cornu@...s.st.com>,
        Maarten Lankhorst
	<maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Rob Herring <robh@...nel.org>,
        "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "Maxime
 Coquelin" <mcoquelin.stm32@...il.com>,
        Alexandre Torgue
	<alexandre.torgue@...s.st.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Christophe Roullier
	<christophe.roullier@...s.st.com>
CC: <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 08/13] drm/stm: ltdc: handle lvds pixel clock

Hi Raphael,

Thanks for the patch.

Acked-by: Yannick Fertre <yannick.fertre@...s.st.com>

Le 21/08/2025 à 13:08, Raphael Gallais-Pou a écrit :
> From: Yannick Fertre <yannick.fertre@...s.st.com>
>
> Handle LVDS pixel clock.
>
> The LTDC operates with multiple clock domains for register access,
> requiring all clocks to be provided during read/write operations.  This
> imposes a dependency between the LVDS and LTDC to access correctly all
> LTDC registers.  And because both IPs' pixel rates must be synchronized,
> the LTDC has to handle the LVDS clock.
>
> Signed-off-by: Yannick Fertre <yannick.fertre@...s.st.com>
> Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
> ---
>   drivers/gpu/drm/stm/ltdc.c | 22 +++++++++++++++++++++-
>   drivers/gpu/drm/stm/ltdc.h |  1 +
>   2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 17548dd3484a0a3e1015c58c752b80f8892a0ff7..f84a9a8590f0653e422798ff61804d7c3966caef 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -837,6 +837,12 @@ ltdc_crtc_mode_valid(struct drm_crtc *crtc,
>   	int target_max = target + CLK_TOLERANCE_HZ;
>   	int result;
>   
> +	if (ldev->lvds_clk) {
> +		result = clk_round_rate(ldev->lvds_clk, target);
> +		drm_dbg_driver(crtc->dev, "lvds pixclk rate target %d, available %d\n",
> +			       target, result);
> +	}
> +
>   	result = clk_round_rate(ldev->pixel_clk, target);
>   
>   	DRM_DEBUG_DRIVER("clk rate target %d, available %d\n", target, result);
> @@ -1878,6 +1884,8 @@ void ltdc_suspend(struct drm_device *ddev)
>   	clk_disable_unprepare(ldev->pixel_clk);
>   	if (ldev->bus_clk)
>   		clk_disable_unprepare(ldev->bus_clk);
> +	if (ldev->lvds_clk)
> +		clk_disable_unprepare(ldev->lvds_clk);
>   }
>   
>   int ltdc_resume(struct drm_device *ddev)
> @@ -1895,8 +1903,16 @@ int ltdc_resume(struct drm_device *ddev)
>   
>   	if (ldev->bus_clk) {
>   		ret = clk_prepare_enable(ldev->bus_clk);
> -		if (ret)
> +		if (ret) {
>   			drm_err(ddev, "failed to enable bus clock (%d)\n", ret);
> +			return ret;
> +		}
> +	}
> +
> +	if (ldev->lvds_clk) {
> +		ret = clk_prepare_enable(ldev->lvds_clk);
> +		if (ret)
> +			drm_err(ddev, "failed to prepare lvds clock\n");
>   	}
>   
>   	return ret;
> @@ -1981,6 +1997,10 @@ int ltdc_load(struct drm_device *ddev)
>   		}
>   	}
>   
> +	ldev->lvds_clk = devm_clk_get(dev, "lvds");
> +	if (IS_ERR(ldev->lvds_clk))
> +		ldev->lvds_clk = NULL;
> +
>   	rstc = devm_reset_control_get_exclusive(dev, NULL);
>   
>   	mutex_init(&ldev->err_lock);
> diff --git a/drivers/gpu/drm/stm/ltdc.h b/drivers/gpu/drm/stm/ltdc.h
> index ddfa8ae61a7ba5dc446fae647562d0ec8e6953e1..17b51a7ce28eee5de6d24ca943ca3b1f48695dfd 100644
> --- a/drivers/gpu/drm/stm/ltdc.h
> +++ b/drivers/gpu/drm/stm/ltdc.h
> @@ -48,6 +48,7 @@ struct ltdc_device {
>   	void __iomem *regs;
>   	struct regmap *regmap;
>   	struct clk *pixel_clk;	/* lcd pixel clock */
> +	struct clk *lvds_clk;	/* lvds pixel clock */
>   	struct clk *bus_clk;	/* bus clock */
>   	struct mutex err_lock;	/* protecting error_status */
>   	struct ltdc_caps caps;
>