[PATCH 1/2] drm: rcar-du: Restrict DPLL duty cycle workaround to H3 ES1.x

[Laurent Pinchart]

The H3 ES1.x exhibits dot clock duty cycle stability issues. We can work
around them by configuring the DPLL to twice the desired frequency,
coupled with a /2 post-divider. This isn't needed on other SoCs and
breaks HDMI output on M3-W for a currently unknown reason, so restrict
the workaround to H3 ES1.x.

>From an implementation point of view, move work around handling outside
of the rcar_du_dpll_divider() function by requesting a x2 DPLL output
frequency explicitly. The existing post-divider calculation mechanism
will then take care of dividing the clock by two automatically.

While at it, print a more useful debugging message to ease debugging
clock rate issues.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
---
 drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 37 +++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
index 4ed6f2340af0..9ae0d7b5fb69 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
@@ -13,6 +13,7 @@
 
 #include <linux/clk.h>
 #include <linux/mutex.h>
+#include <linux/sys_soc.h>
 
 #include <drm/drmP.h>
 #include <drm/drm_atomic.h>
@@ -129,10 +130,8 @@ static void rcar_du_dpll_divider(struct rcar_du_crtc *rcrtc,
 			for (fdpll = 1; fdpll < 32; fdpll++) {
 				unsigned long output;
 
-				/* 1/2 (FRQSEL=1) for duty rate 50% */
 				output = input * (n + 1) / (m + 1)
-				       / (fdpll + 1) / 2;
-
+				       / (fdpll + 1);
 				if (output >= 400000000)
 					continue;
 
@@ -158,6 +157,11 @@ static void rcar_du_dpll_divider(struct rcar_du_crtc *rcrtc,
 		 best_diff);
 }
 
+static const struct soc_device_attribute rcar_du_r8a7795_es1[] = {
+	{ .soc_id = "r8a7795", .revision = "ES1.*" },
+	{ /* sentinel */ }
+};
+
 static void rcar_du_crtc_set_display_timing(struct rcar_du_crtc *rcrtc)
 {
 	const struct drm_display_mode *mode = &rcrtc->crtc.state->adjusted_mode;
@@ -185,7 +189,20 @@ static void rcar_du_crtc_set_display_timing(struct rcar_du_crtc *rcrtc)
 
 		extclk = clk_get_rate(rcrtc->extclock);
 		if (rcdu->info->dpll_ch & (1 << rcrtc->index)) {
-			rcar_du_dpll_divider(rcrtc, &dpll, extclk, mode_clock);
+			unsigned long target = mode_clock;
+
+			/*
+			 * The H3 ES1.x exhibits dot clock duty cycle stability
+			 * issues. We can work around them by configuring the
+			 * DPLL to twice the desired frequency, coupled with a
+			 * /2 post-divider. This isn't needed on other SoCs and
+			 * breaks HDMI output on M3-W for a currently unknown
+			 * reason, so restrict the workaround to H3 ES1.x.
+			 */
+			if (soc_device_match(rcar_du_r8a7795_es1))
+				target *= 2;
+
+			rcar_du_dpll_divider(rcrtc, &dpll, extclk, target);
 			extclk = dpll.output;
 		}
 
@@ -197,8 +214,6 @@ static void rcar_du_crtc_set_display_timing(struct rcar_du_crtc *rcrtc)
 
 		if (abs((long)extrate - (long)mode_clock) <
 		    abs((long)rate - (long)mode_clock)) {
-			dev_dbg(rcrtc->group->dev->dev,
-				"crtc%u: using external clock\n", rcrtc->index);
 
 			if (rcdu->info->dpll_ch & (1 << rcrtc->index)) {
 				u32 dpllcr = DPLLCR_CODE | DPLLCR_CLKE
@@ -215,12 +230,14 @@ static void rcar_du_crtc_set_display_timing(struct rcar_du_crtc *rcrtc)
 
 				rcar_du_group_write(rcrtc->group, DPLLCR,
 						    dpllcr);
-
-				escr = ESCR_DCLKSEL_DCLKIN | 1;
-			} else {
-				escr = ESCR_DCLKSEL_DCLKIN | extdiv;
 			}
+
+			escr = ESCR_DCLKSEL_DCLKIN | extdiv;
 		}
+
+		dev_dbg(rcrtc->group->dev->dev,
+			"mode clock %lu extrate %lu rate %lu ESCR 0x%08x\n",
+			mode_clock, extrate, rate, escr);
 	}
 
 	rcar_du_group_write(rcrtc->group, rcrtc->index % 2 ? ESCR2 : ESCR,
-- 
Regards,

Laurent Pinchart