Hi, On Thu, Dec 8, 2022 at 5:48 PM Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> wrote: > > On Thu, Dec 08, 2022 at 05:38:28PM -0800, Dmitry Torokhov wrote: > > On Thu, Dec 08, 2022 at 11:20:06AM -0800, Douglas Anderson wrote: > > > The elan touchscreen datasheet says that the reset GPIO only needs to > > > be asserted for 500us in order to reset the regulator. The problem is > > > that some boards need a level shifter between the signals on the GPIO > > > controller and the signals on the touchscreen. All of these extra > > > components on the line can slow the transition of the signals. On one > > > board, we measured the reset line and saw that it took almost 1.8ms to > > > go low. Even after we bumped up the "drive strength" of the signal > > > from the default 2mA to 8mA we still saw it take 421us for the signal > > > to go low. > > > > > > In order to account for this we let's lengthen the amount of time that > > > we keep the reset asserted. Let's bump it up from 500us to 5000us. > > > That's still a relatively short amount of time and is much safer. > > > > > > It should be noted that this fixes real problems. Case in point: > > > 1. The touchscreen power rail may be shared with another device (like > > > an eDP panel). That means that at probe time power might already be > > > on. > > > 2. In probe we grab the reset GPIO and assert it (make it low). > > > 3. We turn on power (a noop since it was already on). > > > 4. We wait 500us. > > > 5. We deassert the reset GPIO. > > > > > > With the above case and only a 500us delay we saw only a partial reset > > > asserted, which is bad. Giving it 5ms is overkill but feels safer in > > > case someone else has a different level shifter setup. > > > > > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > > > > Applied, thank you. > > Unapplied ;) I guess we should follow kernel test robot's advise and > switch to using usleep_range(). Crud. I'll send a v2 right away. -Doug
