linux-kernel - Re: [PATCH] drm/stm: dsi: relax mode

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Date: Mon, 22 Apr 2024 16:05:31 +0200
From: Sean Nyekjaer <sean@...nix.com>
To: Yannick Fertre <yannick.fertre@...s.st.com>, 
	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>, 
	Daniel Vetter <daniel@...ll.ch>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Robert Foss <rfoss@...nel.org>, 
	Antonio Borneo <antonio.borneo@...s.st.com>
Cc: dri-devel@...ts.freedesktop.org, 
	linux-stm32@...md-mailman.stormreply.com, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/stm: dsi: relax mode_valid clock tolerance

On Fri, Mar 22, 2024 at 11:47:31AM +0100, Sean Nyekjaer wrote:
> When using the DSI interface via DSI2LVDS bridge, it seems a bit harsh
> to reguire the requested and the actual px clock to be within
> 50Hz. A typical LVDS display requires the px clock to be within +-10%.
> 
> In case for HDMI .5% tolerance is required.
> 
> Fixes: e01356d18273 ("drm/stm: dsi: provide the implementation of mode_valid()")
> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> ---
Any feedback on this?

>  drivers/gpu/drm/stm/dw_mipi_dsi-stm.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> index d5f8c923d7bc..97936b0ef702 100644
> --- a/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> +++ b/drivers/gpu/drm/stm/dw_mipi_dsi-stm.c
> @@ -322,8 +322,6 @@ dw_mipi_dsi_phy_get_timing(void *priv_data, unsigned int lane_mbps,
>  	return 0;
>  }
>  
> -#define CLK_TOLERANCE_HZ 50
> -
>  static enum drm_mode_status
>  dw_mipi_dsi_stm_mode_valid(void *priv_data,
>  			   const struct drm_display_mode *mode,
> @@ -375,9 +373,10 @@ dw_mipi_dsi_stm_mode_valid(void *priv_data,
>  		/*
>  		 * Filter modes according to the clock value, particularly useful for
>  		 * hdmi modes that require precise pixel clocks.
> +		 * Check that px_clock is within .5% tolerance.
>  		 */
> -		if (px_clock_hz < target_px_clock_hz - CLK_TOLERANCE_HZ ||
> -		    px_clock_hz > target_px_clock_hz + CLK_TOLERANCE_HZ)
> +		if (px_clock_hz < mult_frac(target_px_clock_hz, 995, 1000) ||
> +		    px_clock_hz > mult_frac(target_px_clock_hz, 1005, 1000))
>  			return MODE_CLOCK_RANGE;
>  
>  		/* sync packets are codes as DSI short packets (4 bytes) */
> -- 
> 2.44.0
>