linux-kernel - [PATCH] drm/bridge: adv7533: Fix adv7533_mode

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Date:   Sat, 11 Mar 2023 17:10:07 -0600
From:   Adam Ford <aford173@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     aford@...conembedded.com, dmitry.baryshkov@...aro.org,
        quic_abhinavk@...cinc.com, Adam Ford <aford173@...il.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>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org
Subject: [PATCH] drm/bridge: adv7533: Fix adv7533_mode_valid for adv7533 and adv7535

When dynamically switching lanes was removed, the intent of the code
was to check to make sure that higher speed items used 4 lanes, but
it had the unintended consequence of removing the slower speeds for
4-lane users.

This attempts to remedy this by doing a check to see that the
max frequency doesn't exceed the chip limit, and a second
check to make sure that the max bit-rate doesn't exceed the
number of lanes * max bit rate / lane.

Fixes: 9a0cdcd6649b ("drm/bridge: adv7533: remove dynamic lane switching from adv7533 bridge")

Signed-off-by: Adam Ford <aford173@...il.com>

diff --git a/drivers/gpu/drm/bridge/adv7511/adv7533.c b/drivers/gpu/drm/bridge/adv7511/adv7533.c
index fdfeadcefe80..10a112d36945 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7533.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7533.c
@@ -103,13 +103,9 @@ void adv7533_dsi_power_off(struct adv7511 *adv)
 enum drm_mode_status adv7533_mode_valid(struct adv7511 *adv,
 					const struct drm_display_mode *mode)
 {
-	int lanes;
+	unsigned long max_lane_freq;
 	struct mipi_dsi_device *dsi = adv->dsi;
-
-	if (mode->clock > 80000)
-		lanes = 4;
-	else
-		lanes = 3;
+	u8 bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
 
 	/*
 	 * TODO: add support for dynamic switching of lanes
@@ -117,8 +113,16 @@ enum drm_mode_status adv7533_mode_valid(struct adv7511 *adv,
 	 * out the modes which shall need different number of lanes
 	 * than what was configured in the device tree.
 	 */
-	if (lanes != dsi->lanes)
-		return MODE_BAD;
+
+	/* Check max clock for either 7533 or 7535 */
+	if (mode->clock > (adv->type == ADV7533 ? 80000 : 148500))
+		return MODE_CLOCK_HIGH;
+
+	/* Check max clock for each lane */
+	max_lane_freq = (adv->type == ADV7533 ? 800000 : 891000);
+
+	if (mode->clock * bpp > max_lane_freq * adv->num_dsi_lanes)
+		return MODE_CLOCK_HIGH;
 
 	return MODE_OK;
 }
-- 
2.37.2