linux-kernel - Re: [PATCH] drm/bridge: imx8mp-hdmi-tx: allow 0.5% margin with selected clock

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Message-ID: <0a8f6921-5b46-4edb-ba96-dee61f4969a6@kontron.de>
Date: Thu, 5 Sep 2024 09:49:25 +0200
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: Dominique Martinet <dominique.martinet@...ark-techno.com>,
 Liu Ying <victor.liu@....com>, 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>,
 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>,
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>
Cc: Adam Ford <aford173@...il.com>, Lucas Stach <l.stach@...gutronix.de>,
 dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: imx8mp-hdmi-tx: allow 0.5% margin with
 selected clock

On 04.09.24 10:31 AM, Dominique Martinet wrote:
> This allows the hdmi driver to pick e.g. 64.8MHz instead of 65Mhz when we
> cannot output the exact frequency, enabling the imx8mp HDMI output to
> support more modes
> 
> Signed-off-by: Dominique Martinet <dominique.martinet@...ark-techno.com>

Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>
Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de>

> ---
> This completes the patch series sent by Adam Ford here:
> https://lkml.kernel.org/r/20240904023310.163371-1-aford173@gmail.com
> 
> and makes the cheap screens we recommend work with our imx8mp board
> without further kludging.
> 
> 
>  drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
> index 13bc570c5473..9431cd5e06c3 100644
> --- a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
> +++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c
> @@ -23,6 +23,7 @@ imx8mp_hdmi_mode_valid(struct dw_hdmi *dw_hdmi, void *data,
>  		       const struct drm_display_mode *mode)
>  {
>  	struct imx8mp_hdmi *hdmi = (struct imx8mp_hdmi *)data;
> +	long round_rate;
>  
>  	if (mode->clock < 13500)
>  		return MODE_CLOCK_LOW;
> @@ -30,8 +31,9 @@ imx8mp_hdmi_mode_valid(struct dw_hdmi *dw_hdmi, void *data,
>  	if (mode->clock > 297000)
>  		return MODE_CLOCK_HIGH;
>  
> -	if (clk_round_rate(hdmi->pixclk, mode->clock * 1000) !=
> -	    mode->clock * 1000)
> +	round_rate = clk_round_rate(hdmi->pixclk, mode->clock * 1000);
> +	/* accept 0.5% = 1/200 = 5/1000 tolerance */
> +	if (abs(round_rate - mode->clock * 1000) > mode->clock * 5)
>  		return MODE_CLOCK_RANGE;
>  
>  	/* We don't support double-clocked and Interlaced modes */