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authorSebastian Reichel <sebastian.reichel@collabora.com>2020-11-27 21:04:29 +0100
committerSam Ravnborg <sam@ravnborg.org>2020-11-29 22:38:12 +0100
commit7c4bada12d320d8648ba3ede6f9b6f9e10f1126a (patch)
treeae8a145e3a0475ddc2a253c8eda61460fc664535
parentaec9fe892812ed10d0bffcf309d2a8fc380d8ce6 (diff)
drm/panel: sony-acx565akm: Fix race condition in probe
The probe routine acquires the reset GPIO using GPIOD_OUT_LOW. Directly afterwards it calls acx565akm_detect(), which sets the GPIO value to HIGH. If the bootloader initialized the GPIO to HIGH before the probe routine was called, there is only a very short time period of a few instructions where the reset signal is LOW. Exact time depends on compiler optimizations, kernel configuration and alignment of the stars, but I expect it to be always way less than 10us. There are no public datasheets for the panel, but acx565akm_power_on() has a comment with timings and reset period should be at least 10us. So this potentially brings the panel into a half-reset state. The result is, that panel may not work after boot and can get into a working state by re-enabling it (e.g. by blanking + unblanking), since that does a clean reset cycle. This bug has recently been hit by Ivaylo Dimitrov, but there are some older reports which are probably the same bug. At least Tony Lindgren, Peter Ujfalusi and Jarkko Nikula have experienced it in 2017 describing the blank/unblank procedure as possible workaround. Note, that the bug really goes back in time. It has originally been introduced in the predecessor of the omapfb driver in commit 3c45d05be382 ("OMAPDSS: acx565akm panel: handle gpios in panel driver") in 2012. That driver eventually got replaced by a newer one, which had the bug from the beginning in commit 84192742d9c2 ("OMAPDSS: Add Sony ACX565AKM panel driver") and still exists in fbdev world. That driver has later been copied to omapdrm and then was used as a basis for this driver. Last but not least the omapdrm specific driver has been removed in commit 45f16c82db7e ("drm/omap: displays: Remove unused panel drivers"). Reported-by: Jarkko Nikula <jarkko.nikula@bitmer.com> Reported-by: Peter Ujfalusi <peter.ujfalusi@ti.com> Reported-by: Tony Lindgren <tony@atomide.com> Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi> Reported-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> Cc: Merlijn Wajer <merlijn@wizzup.org> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> Fixes: 1c8fc3f0c5d2 ("drm/panel: Add driver for the Sony ACX565AKM panel") Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com> Tested-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi> Tested-by: Jarkko Nikula <jarkko.nikula@bitmer.com> Signed-off-by: Sam Ravnborg <sam@ravnborg.org> Link: https://patchwork.freedesktop.org/patch/msgid/20201127200429.129868-1-sebastian.reichel@collabora.com
-rw-r--r--drivers/gpu/drm/panel/panel-sony-acx565akm.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/gpu/drm/panel/panel-sony-acx565akm.c b/drivers/gpu/drm/panel/panel-sony-acx565akm.c
index e95fdfb16b6c..ba0b3ead150f 100644
--- a/drivers/gpu/drm/panel/panel-sony-acx565akm.c
+++ b/drivers/gpu/drm/panel/panel-sony-acx565akm.c
@@ -629,7 +629,7 @@ static int acx565akm_probe(struct spi_device *spi)
lcd->spi = spi;
mutex_init(&lcd->mutex);
- lcd->reset_gpio = devm_gpiod_get(&spi->dev, "reset", GPIOD_OUT_LOW);
+ lcd->reset_gpio = devm_gpiod_get(&spi->dev, "reset", GPIOD_OUT_HIGH);
if (IS_ERR(lcd->reset_gpio)) {
dev_err(&spi->dev, "failed to get reset GPIO\n");
return PTR_ERR(lcd->reset_gpio);