The ili9486 driver uses DRM_SIMPLE_MODE() which sets the pixel
clock to 1 kHz. Since htotal==hdisplay and vtotal==vdisplay,
the calculated vrefresh is:
1000 / (480 * 320) = 0.006 Hz
This breaks Wayland compositors in two ways. Compositors that
use the mode's refresh rate to schedule their repaint loop
(such as Weston) compute a repaint delay of over a second,
triggering abnormal delay warnings and degrading rendering.
Compositors that are page-flip driven (such as wlroots-based
compositors) are unaffected at the compositor level, but still
report the near-zero rate to clients via wl_output.mode. This
causes toolkits such as GTK4 to not schedule redraws, so
applications render their initial frame but never visually
update in response to input.
Replace DRM_SIMPLE_MODE() with DRM_MODE_INIT(30, ...) which
properly calculates the pixel clock for a 30 Hz target refresh
rate. 30 Hz is a conservative default achievable on most SPI
setups. The actual frame rate remains bounded by SPI bus
throughput; the mode's vrefresh only affects how compositors
and clients schedule rendering.
Note: other tiny DRM drivers (hx8357d, ili9163, ili9225,
ili9341, mi0283qt, repaper, sharp-memory) have the same issue
and would benefit from the same change.
Tested on Raspberry Pi 4 with ILI9486-based MHS-3.5" SPI LCD
(480x320). With Weston, the compositor logs "computed repaint
delay is abnormal" warnings. With sway (wlroots), GTK4 clients
fail to visually update. Both issues are resolved by this
patch.
Signed-off-by: Belousov Maksim <[email protected]>
---
drivers/gpu/drm/tiny/ili9486.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/tiny/ili9486.c b/drivers/gpu/drm/tiny/ili9486.c
index 1e411a0f4..83eda43bd 100644
--- a/drivers/gpu/drm/tiny/ili9486.c
+++ b/drivers/gpu/drm/tiny/ili9486.c
@@ -165,7 +165,7 @@ static const struct drm_simple_display_pipe_funcs
waveshare_pipe_funcs = {
};
static const struct drm_display_mode waveshare_mode = {
- DRM_SIMPLE_MODE(480, 320, 73, 49),
+ DRM_MODE_INIT(30, 480, 320, 73, 49),
};
DEFINE_DRM_GEM_DMA_FOPS(ili9486_fops);
--
2.51.0
