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

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Message-Id: <20240904083103.1257480-1-dominique.martinet@atmark-techno.com>
Date: Wed,  4 Sep 2024 17:31:01 +0900
From: Dominique Martinet <dominique.martinet@...ark-techno.com>
To: 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>,
	Frieder Schrempf <frieder.schrempf@...tron.de>,
	Dominique Martinet <dominique.martinet@...ark-techno.com>,
	dri-devel@...ts.freedesktop.org,
	imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] drm/bridge: imx8mp-hdmi-tx: allow 0.5% margin with selected clock

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>
---
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 */
-- 
2.39.2