[PATCH V2] drm/bridge: adv7533: Fix adv7533_mode_valid for adv7533 and adv7535

[Adam Ford <aford173@gmail.com>]

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")
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Adam Ford <aford173@gmail.com>
---

V2:  Fix whitespace in comment
     Remove TODO comment
     Add R-B from Robert.

diff --git a/drivers/gpu/drm/bridge/adv7511/adv7533.c b/drivers/gpu/drm/bridge/adv7511/adv7533.c
index fdfeadcefe80..7e3e56441aed 100644
--- a/drivers/gpu/drm/bridge/adv7511/adv7533.c
+++ b/drivers/gpu/drm/bridge/adv7511/adv7533.c
@@ -103,22 +103,19 @@ 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;
+	u8 bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
 
-	if (mode->clock > 80000)
-		lanes = 4;
-	else
-		lanes = 3;
-
-	/*
-	 * TODO: add support for dynamic switching of lanes
-	 * by using the bridge pre_enable() op . Till then filter
-	 * 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;
 }
-- 
2.34.1