| Message ID | 20221208111910.1.I39c387f1e3176fcf340039ec12d54047de9f8526@changeid |
|---|---|
| State | Superseded |
| Headers | show |
| Series | arm64: dts: qcom: sc7180: Make pazquel360's touchscreen work | expand |
On Thu, Dec 08, 2022 at 11:20:02AM -0800, Douglas Anderson wrote: > 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>
diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi index f1defb94d670..ff1c7aa6a722 100644 --- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi +++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi @@ -1376,7 +1376,15 @@ ts_reset_l: ts-reset-l-state { 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 {
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> --- arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)