Hi Michael, Andy, On Fri, 2021-05-28 at 08:37 +0200, Michael Walle wrote: > Am 2021-05-24 13:41, schrieb Sander Vanheule: > > Hi Andy, Andrew, > > > > On Mon, 2021-05-24 at 10:53 +0300, Andy Shevchenko wrote: > > > On Mon, May 24, 2021 at 4:11 AM Andrew Lunn <andrew@xxxxxxx> wrote: > > > > > > > > > Changes since v2: > > > > > - MDIO regmap support was merged, so patch is dropped here > > > > > > > > Do you have any idea how this will get merged. It sounds like one of > > > > the Maintainers will need a stable branch of regmap. > > > > > > This is not a problem if Mark provides an immutable branch to pull > > > from. > > > > Mark has a tag (regmap-mdio) for this patch: > > https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap.git/tag/?h=regmap-mdio > > > > > > > > > > - Introduce GPIO regmap quirks to set output direction first > > > > > > > > I thought you had determined it was possible to set output before > > > > direction? > > > > > > Same thoughts when I saw an updated version of that patch. My > > > anticipation was to not see it at all. > > > > The two devices I've been trying to test the behaviour on are: > > * Netgear GS110TPP: has an RTL8231 with three LEDs, each driven via a > > pin > > configured as (active-low) GPIO. The LEDs are easy for a quick > > visual check. > > * Zyxel GS1900-8: RTL8231 used for the front panel button, and an > > active-low > > GPIO used to hard reset the main SoC (an RTL8380). I've modified > > this board > > to change some of the strapping pin values, but testing with the > > jumpers and > > pull-up/down resistors is a bit more tedious. > > > > On the Netgear, I tested the following with and without the quirk: > > > > # Set as OUT-LOW twice, to avoid the quirk. Always turns the LED on > > gpioset 1 32=0; gpioset 1 32=0 > > # Get value to change to input, turns the LED off (high impedance) > > # Will return 1 due to (weak) internal pull-up > > gpioget 1 32 > > # Set as OUT-HIGH, should result in LED off > > # When the quirk is disabled, the LED turns on (i.e. old OUT-LOW > > value) > > # When the quirk is enabled, the LED remains off (i.e. correct > > OUT-HIGH value) > > gpioset 1 32=1 > > > > Now, what's confusing (to me) is that the inverse doesn't depend on the > > quirk: > > > > # Set as OUT-HIGH twice > > gpioset 1 32=1; gpioset 1 32=1 > > # Change to high-Z > > gpioget 1 32 > > # Set to OUT-LOW, always results in LED on, with or without quirk > > gpioset 1 32=0 > > > > Any idea why this would be (or appear) broken on the former case, but > > not on the > > latter? > > Before reading this, I'd have guessed that they switch the internal > register > depending on the GPIO direction; I mean there is only one register > address > for both the input and the output register. Hm. > > Did you try playing around with raw register accesses and see if the > value > of the GPIO data register is changing when you switch GPIOs to > input/output. > > Eg. you could try https://github.com/kontron/miitool to access the > registers > from userspace (your ethernet controller has to have support for the > ioctl's > though, see commit a613bafec516 ("enetc: add ioctl() support for > PHY-related > ops") for an example). I think I found a solution! As Michael suggested, I tried raw register reads and writes, to eliminate any side effects of the intermediate code. I didn't use the ioctls (this isn't a netdev), but I found regmap's debugfs write functionality, which allowed me to do the same. I was trying to reproduce the behaviour I reported earlier, but couldn't. The output levels were always the intended ones. At some point I realised that the regmap_update_bits function does a read-modify-write, which might shadow the actual current output value. For example: * Set output low: current out is low * Change to input with pull-up: current out is still low, but DATAx reads high * Set output high: RMW reads a high value (the input), so assumes a write is not necessary, leaving the old output value (low). Currently, I see two options: * Use regmap_update_bits_base to avoid the lazy RMW behaviour * Add a cache for the output data values to the driver, and only use these values to write to the output registers. This would allow keeping lazy RMW behaviour, which may be a benefit on slow busses. With either of these implemented, if I set the output value before the direction, everything works! :-) Would you like this to be added to regmap-gpio, or should I revert back to a device-specific implementation? Best, Sander
