Commit e02b5262fd28 ("drm/bridge: it66121: acquire reset GPIO in probe")
rightfully added code to make the reset pin really work instead of being a
no-op, but that change introduced a regression making probe fail most of
the times, at least on some hardware.
On a BeagleBone Black rev.D the IT66122 silently fails probing >90% of the
times. This is because:
1. the regmap_read() calls just after it66121_hw_reset() to read the ID
registers fail
2. there is no error checking for these regmap_read(), execution
continues silently
3. this results in not matching any of the IDs from it66xx_chip_info
4. and this results in silently returning -ENODEV
Empirical tests showed a small delay after de-asserting reset fixes
probing. Likely the device needs some ramp-up time after reset. No such
requirement is mentioned in the docs I could find, so the amount of delay
was chosen by testing: 10 ms worked in 100% of 25 test runs, so setting a
20 ms delay should provide a safe margin.
Fixes: e02b5262fd28 ("drm/bridge: it66121: acquire reset GPIO in probe")
Cc: [email protected]
Signed-off-by: Luca Ceresoli <[email protected]>
---
FYI For items 2 and 4 above, I'm sending separate patches to make those
errors not silent. Those aren't fixes, so they would be for drm-misc-next,
while this patch is for drm-misc-fixes.
---
drivers/gpu/drm/bridge/ite-it66121.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/bridge/ite-it66121.c
b/drivers/gpu/drm/bridge/ite-it66121.c
index 51fc68ffdf8f..692a85e1e2e8 100644
--- a/drivers/gpu/drm/bridge/ite-it66121.c
+++ b/drivers/gpu/drm/bridge/ite-it66121.c
@@ -356,6 +356,7 @@ static void it66121_hw_reset(struct it66121_ctx *ctx)
gpiod_set_value(ctx->gpio_reset, 1);
msleep(20);
gpiod_set_value(ctx->gpio_reset, 0);
+ msleep(20);
}
static inline int it66121_preamble_ddc(struct it66121_ctx *ctx)
---
base-commit: 20b91781216dc693d862368b523e752525172176
change-id: 20261015-drm-ite-it66121-fix-reset-f1765358a866
Best regards,
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
