linux-kernel - [PATCH v2 5/6] drm/panel: st7703: Drive XBD599 panel at higher clock rate

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Message-Id: <20240205-pinephone-pll-fixes-v2-5-96a46a2d8c9b@oltmanns.dev>
Date: Mon, 05 Feb 2024 16:22:28 +0100
From: Frank Oltmanns <frank@...manns.dev>
To: Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, Chen-Yu Tsai <wens@...e.org>, 
 Jernej Skrabec <jernej.skrabec@...il.com>, 
 Samuel Holland <samuel@...lland.org>, 
 Guido Günther <agx@...xcpu.org>, 
 Purism Kernel Team <kernel@...i.sm>, Ondrej Jirman <megi@....cz>, 
 Neil Armstrong <neil.armstrong@...aro.org>, 
 Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>, 
 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>, 
 Rob Herring <robh+dt@...nel.org>, 
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
 Conor Dooley <conor+dt@...nel.org>
Cc: linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
 Frank Oltmanns <frank@...manns.dev>
Subject: [PATCH v2 5/6] drm/panel: st7703: Drive XBD599 panel at higher
 clock rate

This panel is used in the pinephone that runs on a Allwinner A64 SOC.
The SOC requires pll-mipi to run at more than 500 MHz.

This is the relevant clock tree:
 pll-mipi
    tcon0
       tcon-data-clock

tcon-data-clock has to run at 1/4 the DSI per-lane bit rate. The XBD599
has 24 bpp and 4 lanes. Therefore, the resulting requested
tcon-data-clock rate is:
    crtc_clock * 1000 * (24 / 4) / 4

tcon-data-clock runs at tcon0 / 4 (fixed divisor), so it requests a
parent rate of
    4 * (crtc_clock * 1000 * (24 / 4) / 4)

Since tcon0 is a ccu_mux, the rate of tcon0 equals the rate of pll-mipi.

pll-mipi's constraint to run at 500MHz or higher forces us to have a
crtc_clock >= 83333 kHz if we want a 60 Hz vertical refresh rate.

Change [hv]sync_(start|end) so that we reach a clock rate of 83502 kHz
so that it is high enough to align with pll-pipi limits.

Signed-off-by: Frank Oltmanns <frank@...manns.dev>
---
 drivers/gpu/drm/panel/panel-sitronix-st7703.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-sitronix-st7703.c b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
index b55bafd1a8be..6886fd7f765e 100644
--- a/drivers/gpu/drm/panel/panel-sitronix-st7703.c
+++ b/drivers/gpu/drm/panel/panel-sitronix-st7703.c
@@ -320,14 +320,14 @@ static int xbd599_init_sequence(struct st7703 *ctx)
 
 static const struct drm_display_mode xbd599_mode = {
 	.hdisplay    = 720,
-	.hsync_start = 720 + 40,
-	.hsync_end   = 720 + 40 + 40,
-	.htotal	     = 720 + 40 + 40 + 40,
+	.hsync_start = 720 + 65,
+	.hsync_end   = 720 + 65 + 65,
+	.htotal      = 720 + 65 + 65 + 65,
 	.vdisplay    = 1440,
-	.vsync_start = 1440 + 18,
-	.vsync_end   = 1440 + 18 + 10,
-	.vtotal	     = 1440 + 18 + 10 + 17,
-	.clock	     = 69000,
+	.vsync_start = 1440 + 30,
+	.vsync_end   = 1440 + 30 + 22,
+	.vtotal	     = 1440 + 30 + 22 + 29,
+	.clock	     = (720 + 65 + 65 + 65) * (1440 + 30 + 22 + 29) * 60 / 1000,
 	.flags	     = DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC,
 	.width_mm    = 68,
 	.height_mm   = 136,

-- 
2.43.0