linux-kernel - Re: [PATCH] drm/stm: ltdc: use crtc_mode_fixup to update adjusted

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Message-ID: <1617432.LU6HsMfOQM@avalon>
Date:   Mon, 29 Jan 2018 12:43:31 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Philippe Cornu <philippe.cornu@...com>
Cc:     Yannick Fertre <yannick.fertre@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Vincent Abriou <vincent.abriou@...com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Fabien Dessenne <fabien.dessenne@...com>,
        Mickael Reulier <mickael.reulier@...com>,
        Ludovic Barre <ludovic.barre@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>
Subject: Re: [PATCH] drm/stm: ltdc: use crtc_mode_fixup to update adjusted_mode clock

Hi Philippe,

On Thursday, 25 January 2018 18:01:01 EET Philippe Cornu wrote:
> There is a difference between the panel/bridge requested pixel clock
> value and the real one due to the hw platform clock preciseness (pll,
> dividers...). This patch updates the adjusted_mode clock value with
> the real hw clock value so then attached encoder & connector can use
> it for precise timing computations.
> 
> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
> ---
>  drivers/gpu/drm/stm/ltdc.c | 35 +++++++++++++++++++++++++----------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index b48589343ae1..90b3de516c91 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -428,12 +428,35 @@ static void ltdc_crtc_atomic_disable(struct drm_crtc
> *crtc, reg_set(ldev->regs, LTDC_SRCR, SRCR_IMR);
>  }
> 
> +static bool ltdc_crtc_mode_fixup(struct drm_crtc *crtc,
> +				 const struct drm_display_mode *mode,
> +				 struct drm_display_mode *adjusted_mode)
> +{
> +	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
> +	int rate = mode->clock * 1000;
> +
> +	/*
> +	 * TODO clk_round_rate() does not work yet. When ready, it can
> +	 * be used instead of clk_set_rate() then clk_get_rate().
> +	 */

Why does it fail ? Is it due to the STM clock source implementation ? This 
looks like a big hack, I'd rather see clk_round_rate() being fixed.

> +	clk_disable(ldev->pixel_clk);
> +	if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
> +		DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
> +		return false;
> +	}
> +	clk_enable(ldev->pixel_clk);
> +
> +	adjusted_mode->clock = clk_get_rate(ldev->pixel_clk) / 1000;
> +
> +	return true;
> +}
> +
>  static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
>  {
>  	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
>  	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
>  	struct videomode vm;
> -	int rate = mode->clock * 1000;
>  	u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
>  	u32 total_width, total_height;
>  	u32 val;
> @@ -456,15 +479,6 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc
> *crtc) total_width = accum_act_w + vm.hfront_porch;
>  	total_height = accum_act_h + vm.vfront_porch;
> 
> -	clk_disable(ldev->pixel_clk);
> -
> -	if (clk_set_rate(ldev->pixel_clk, rate) < 0) {
> -		DRM_ERROR("Cannot set rate (%dHz) for pixel clk\n", rate);
> -		return;
> -	}
> -
> -	clk_enable(ldev->pixel_clk);
> -
>  	/* Configures the HS, VS, DE and PC polarities. Default Active Low */
>  	val = 0;
> 
> @@ -528,6 +542,7 @@ static void ltdc_crtc_atomic_flush(struct drm_crtc
> *crtc, }
> 
>  static const struct drm_crtc_helper_funcs ltdc_crtc_helper_funcs = {
> +	.mode_fixup = ltdc_crtc_mode_fixup,
>  	.mode_set_nofb = ltdc_crtc_mode_set_nofb,
>  	.atomic_flush = ltdc_crtc_atomic_flush,
>  	.atomic_enable = ltdc_crtc_atomic_enable,

-- 
Regards,

Laurent Pinchart