On Wed, Feb 13, 2019 at 12:43:46PM +0100, Harald Geyer wrote: > Hi Maxime! > > Maxime Ripard writes: > > On Tue, Feb 12, 2019 at 08:37:36PM +0100, Harald Geyer wrote: > > > > There's a few issues with that approach as well: > > > > > > > > - We're actively trying to remove the pinctrl nodes for the GPIOs > > > > > > For what reason? Maybe it doesn't apply to this usecase? > > > > This is kind of separate. At the moment, on all our SoCs but the H6, > > requesting a pin to a separate state using pinctrl doesn't mark the > > GPIO muxed on that pin as reserved, so through the GPIO userspace > > interface (or calling gpio_request from within the kernel, but that > > seems less of a risk) anyone is free to just request a GPIO on a pin > > already requested, behind the consumer drivers' back. Which is pretty > > bad. > > Really, I'm surprised. This is not the behaviour I remember from A20 > and A64. Indeed, testing this on teres with the debug detect pin claimed > by audio, I get: > > root@teres:/sys/kernel/debug/pinctrl/1f02c00.pinctrl# cat pinmux-pins > Pinmux settings per pin > Format: pin (name): mux_owner|gpio_owner (strict) hog? > pin 352 (PL0): device 1f03400.rsb function s_rsb group PL0 > pin 353 (PL1): device 1f03400.rsb function s_rsb group PL1 > pin 354 (PL2): GPIO 1f02c00.pinctrl:354 > pin 355 (PL3): UNCLAIMED > pin 356 (PL4): UNCLAIMED > pin 357 (PL5): UNCLAIMED > pin 358 (PL6): UNCLAIMED > pin 359 (PL7): GPIO 1f02c00.pinctrl:359 > pin 360 (PL8): GPIO 1f02c00.pinctrl:360 > pin 361 (PL9): device sound function gpio_out group PL9 > pin 362 (PL10): UNCLAIMED > pin 363 (PL11): UNCLAIMED > pin 364 (PL12): GPIO 1f02c00.pinctrl:364 > [...] > > root@teres:/sys/class/gpio# echo 361 >export > bash: echo: Schreibfehler: Das Argument ist ungültig. > > So I can't access this from sysfs, even though the error code is a > bit odd: I'd expect EBUSY instead of EINVAL. I can export any of the > UNCLAIMED pins/gpios. > > Trying with libgpiod as well, I see that the state of the pin is reported > incorretly, but I still can't access it: > > gpiochip0 - 32 lines: > line 0: unnamed unused input active-high > line 1: unnamed unused input active-high > line 2: unnamed "reset" output active-low [used] > line 3: unnamed unused input active-high > line 4: unnamed unused input active-high > line 5: unnamed unused input active-high > line 6: unnamed unused input active-high > line 7: unnamed "usb1-vbus" output active-high [used] > line 8: unnamed "Lid Switch" input active-low [used] > line 9: unnamed unused input active-high > line 10: unnamed "sysfs" input active-high [used] > line 11: unnamed unused input active-high > line 12: unnamed "enable" output active-high [used] > line 13: unnamed unused input active-high > > root@teres:~# gpioget 1f02c00.pinctrl 9 > gpioget: error reading GPIO values: Invalid argument > > On a pin exported to sysfs I get EBUSY as expected: > root@teres:~# gpioget 1f02c00.pinctrl 10 > gpioget: error reading GPIO values: Device or resource busy > > And reading an unclaimed pin works as expected too: > root@teres:~# gpioget 1f02c00.pinctrl 11 > 0 > > Either I misunderstood what you have written or it isn't true. This happens when you have a pin requested in pinctrl, but for a function that isn't a GPIO, and you try to request the GPIO on that pin. In you example, such a case can happen if you do sed s/364/361/. Since this is the PMIC, you should probably test this on some other device though :) > > There's support for such a check in pinctrl, and we did enable it for > > the H6. However, one of its side effect is that you can't have a > > pinctrl node for a GPIO anymore (at least without significantly > > reworking the GPIO API in the kernel). > > Can you point me to some background reading? Background reading for what? > > We did enable it for the H6, since it didn't have any backward > > compatibility to take care of, but it's disabled at the moment for all > > the other SoCs to be able to flip that switch at some point. And > > that's why we're moving away from it as well. > > Well ... that's good to know, because I have a couple of custom DTs > with pinctrl nodes for a GPIO. I think it should be documented as > deprecated in the binding then. It's not documented anywhere that we need it. > Also I wonder how I can select drive strength or bias on a gpio line when > I can't use pinctrl with them anymore. That's one of the items we need to take care of as well, yes, but that can be handled through a GPIO flag in the descriptor. There's a series currently taking care of the bias: https://www.spinics.net/lists/linux-gpio/msg36444.html > > > I think the real downside of this approach is, that using the UART > > > makes the internal speakers/mic unuseable too. > > > > That's also a pretty big issue. > > I certainly agree it's unfortunate. > > > > But we need a way to control the mux from userspace and aside from > > > unbinding the ideas proposed thus far are: > > > > > > a) control the gpio directly > > > b) control the gpio via leds-gpio > > > > > > (a) was dismissed because we can't set a default from DT > > > (b) was dismissed because some rogue app might try to blink it > > > > > > The clean solution might be to write mux-gpio, which is actually > > > identical to leds-gpio but lives in /sys/class/mux_switches/ and > > > uses different filenames. But that's going down the "invent a new > > > subsystem road", which I believe is overkill for what is a debugging > > > facility for a single board. > > > > I still believe we should aim at supporting this through pinctrl, and > > adding an userspace API is definitely easier than a full subsystem. > > Getting everybody to agree on a new API (especially a userspace ABI) > is a major headache (and rightly so, we want to get something right on > the first attempt that is going to stay around forever). I don't think > some quirky debugging feature is worth the effort. > > And frankly I don't care much about audio on the teres. I started > working on this because I feel kind of responsible for keeping the > teres DT up-to-date with what the kernel can support. But if the > kernel can't support it ATM: so be it. > > As a compromise I think we could add all the nodes to the DT but mark > their status as "disabled". That would help everybody wanting to enable > audio but still be technically correct. I understand if you don't want to go after that goal yourself, but that doesn't sound practical either. Especially since the A64, more and more people are putting the DT in a ROM, so we can't just change it as we wish. Maxime -- Maxime Ripard, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
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