[PATCH] drm/msm/dsi: round the byte clock rate after reparenting to the PHY PLL

[Dmitry Baryshkov]

DSI 6G v2.9 hosts (SM8650, SM8750, Kaanapali, etc.) reparent the byte and
pixel RCGs to the DSI PHY PLL at runtime from
dsi_link_clk_set_rate_6g_v2_9(), after the PHY has been enabled. However
dsi_calc_clk_rate_6g() runs earlier, in order to compute the bit clock
request for the PHY. At that point the byte RCG still has its reset
parent (XO), so clk_round_rate() returns a bogus rate, which then ends up
in the PHY bit clock request and the PLL gets programmed to a wrong
frequency, breaking the panel.

Move the rounding to dsi_link_clk_set_rate_6g(), which is called after
the RCGs have been reparented to the PLL. Storing the rounded rate at
this point still makes later link_clk_set_rate() calls no-ops in the
CCF. Derive the byte interface clock rate from the rounded byte clock
rate, otherwise it would keep requesting the idealized rate and
retrigger the PLL on every transfer.

Reported-by: Abel Vesa <abel.vesa@xxxxxxxxxxxxxxxx>
Reported-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxxxxxxxx>
Fixes: 6cd33b6f4155 ("drm/msm/dsi: round 6G byte clock rate to the PLL-achievable value")
Assisted-by: LLM
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 7e4e3718b536..b292dfd266d1 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -129,7 +129,7 @@ struct msm_dsi_host {
 	struct clk *dsi_pll_pixel_clk;
 
 	unsigned long byte_clk_rate;
-	unsigned long byte_intf_clk_rate;
+	bool byte_intf_clk_div_2;
 	unsigned long pixel_clk_rate;
 	unsigned long esc_clk_rate;
 
@@ -382,8 +382,20 @@ int msm_dsi_runtime_resume(struct device *dev)
 
 int dsi_link_clk_set_rate_6g(struct msm_dsi_host *msm_host)
 {
+	unsigned long byte_intf_clk_rate;
+	long rounded_byte_clk_rate;
 	int ret;
 
+	rounded_byte_clk_rate = clk_round_rate(msm_host->byte_clk,
+					       msm_host->byte_clk_rate);
+	if (rounded_byte_clk_rate < 0) {
+		pr_err("%s: failed to round byte clock rate, %ld\n",
+		       __func__, rounded_byte_clk_rate);
+		return rounded_byte_clk_rate;
+	}
+
+	msm_host->byte_clk_rate = rounded_byte_clk_rate;
+
 	DBG("Set clk rates: pclk=%lu, byteclk=%lu",
 	    msm_host->pixel_clk_rate, msm_host->byte_clk_rate);
 
@@ -401,7 +413,11 @@ int dsi_link_clk_set_rate_6g(struct msm_dsi_host *msm_host)
 	}
 
 	if (msm_host->byte_intf_clk) {
-		ret = clk_set_rate(msm_host->byte_intf_clk, msm_host->byte_intf_clk_rate);
+		byte_intf_clk_rate = msm_host->byte_clk_rate;
+		if (msm_host->byte_intf_clk_div_2)
+			byte_intf_clk_rate /= 2;
+
+		ret = clk_set_rate(msm_host->byte_intf_clk, byte_intf_clk_rate);
 		if (ret) {
 			pr_err("%s: Failed to set rate byte intf clk, %d\n",
 			       __func__, ret);
@@ -669,24 +685,12 @@ static void dsi_calc_pclk(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 
 int dsi_calc_clk_rate_6g(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
 {
-	long rounded_byte_clk_rate;
-
 	if (!msm_host->mode) {
 		pr_err("%s: mode not set\n", __func__);
 		return -EINVAL;
 	}
 
 	dsi_calc_pclk(msm_host, is_bonded_dsi);
-
-	rounded_byte_clk_rate = clk_round_rate(msm_host->byte_clk,
-					       msm_host->byte_clk_rate);
-	if (rounded_byte_clk_rate < 0) {
-		pr_err("%s: failed to round byte clock rate, %ld\n",
-		       __func__, rounded_byte_clk_rate);
-		return rounded_byte_clk_rate;
-	}
-
-	msm_host->byte_clk_rate = rounded_byte_clk_rate;
 	msm_host->esc_clk_rate = clk_get_rate(msm_host->esc_clk);
 	return 0;
 }
@@ -2495,9 +2499,7 @@ int msm_dsi_host_power_on(struct mipi_dsi_host *host,
 		goto unlock_ret;
 	}
 
-	msm_host->byte_intf_clk_rate = msm_host->byte_clk_rate;
-	if (phy_shared_timings->byte_intf_clk_div_2)
-		msm_host->byte_intf_clk_rate /= 2;
+	msm_host->byte_intf_clk_div_2 = phy_shared_timings->byte_intf_clk_div_2;
 
 	msm_dsi_sfpb_config(msm_host, true);
 

---
base-commit: a9117574de38e27355ded76850df9200ce7870e6
change-id: 20260903-fix-eliza-dsi-8bc2fed2c29b

Best regards,
--  
With best wishes
Dmitry