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| author | Douglas Anderson <dianders@chromium.org> | 2022-12-09 09:12:37 -0800 |
|---|---|---|
| committer | Bjorn Andersson <andersson@kernel.org> | 2022-12-27 21:31:47 -0600 |
| commit | 9506a3661258d07a60b186f667b391708ddf63ac (patch) | |
| tree | fdfe1e333487ec1cdefd9e3ad492fbc6be00f84f | |
| parent | 1c170714490e4d8c0886019145c9d90dfade14f9 (diff) | |
| download | lwn-9506a3661258d07a60b186f667b391708ddf63ac.tar.gz lwn-9506a3661258d07a60b186f667b391708ddf63ac.zip | |
arm64: dts: qcom: sc7180: Bump up trogdor ts_reset_l drive strength
On at least one board (pazquel360) the reset line for the touchscreen
was scoped and found to take almost 2 ms to fall when we drove it
low. This wasn't great because the Linux driver for the touchscreen
(the elants_i2c driver) thinks it can do a 500 us reset pulse. If we
bump the drive strength to 8 mA then the reset line went down in ~421
us.
NOTE: we could apply this fix just for pazquel360, but:
* Probably other trogdor devices have similar timings and it's just
that nobody has noticed it before.
* There are other trogdor boards using the same elan driver that tries
to do 500 us reset pulses.
* Bumping the drive strength to 8mA across the board won't hurt. This
isn't a high speed signal or anything.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221209091234.v3.1.I39c387f1e3176fcf340039ec12d54047de9f8526@changeid
| -rw-r--r-- | arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi index d134d172a3c5..670a7d174e5d 100644 --- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi +++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi @@ -1394,7 +1394,15 @@ ap_spi_fp: &spi10 { pins = "gpio8"; function = "gpio"; bias-disable; - drive-strength = <2>; + + /* + * The reset GPIO to the touchscreen takes almost 2ms to drop + * at the default drive strength. When we bump it up to 8mA it + * falls in under 500us. We want this to be fast since the Elan + * datasheet (and any drivers written based on it) talk about using + * a 500 us reset pulse. + */ + drive-strength = <8>; }; sdc1_on: sdc1-on-state { |