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

Frank Oltmanns
2024-02-05T15:23:18Z

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@oltmanns.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