On Fri, 2022-07-15 at 15:05 +0300, Andy Shevchenko wrote: > On Fri, Jul 15, 2022 at 12:20:56PM +0200, Nuno Sá wrote: > > On Thu, 2022-07-14 at 21:57 +0300, Andy Shevchenko wrote: > > > On Thu, Jul 14, 2022 at 05:43:41PM +0200, Nuno Sá wrote: > > > > On Thu, 2022-07-14 at 17:58 +0300, Andy Shevchenko wrote: > > > > > On Wed, Jul 13, 2022 at 03:14:17PM +0200, Nuno Sá wrote: > > > > > > The gpio core looks at 'FLAG_BIAS_DISABLE' in preparation > > > > > > of > > > > > > calling the > > > > > > gpiochip 'set_config()' hook. However, AFAICT, there's no > > > > > > way > > > > > > that > > > > > > this > > > > > > flag is set because there's no support for it in firwmare > > > > > > code. > > > > > > Moreover, > > > > > > in 'gpiod_configure_flags()', only pull-ups and pull-downs > > > > > > are > > > > > > being > > > > > > handled. > > > > > > > > > > > > On top of this, there are some users that are looking at > > > > > > 'PIN_CONFIG_BIAS_DISABLE' in the 'set_config()' hook. So, > > > > > > unless > > > > > > I'm > > > > > > missing something, it looks like this was never working for > > > > > > these > > > > > > chips. > > > > > > > > > > > > Note that the ACPI case is only compiled tested. At first > > > > > > glance, > > > > > > it seems > > > > > > the current patch is enough but i'm not really sure... > > > > > > > > > > So, I looked closer to the issue you are trying to describe > > > > > here. > > > > > > > > > > As far as I understand we have 4 state of BIAS in the > > > > > hardware: > > > > > 1/ AS IS (defined by firnware) > > > > > 2/ Disabled (neither PU, not PD) > > > > > 3/ PU > > > > > 4/ PD > > > > > > > > > > The case when the default of bias is not disabled (for > > > > > example > > > > > specific, and I > > > > > think very special, hardware may reset it to PD or PU), it's > > > > > a > > > > > hardware driver > > > > > responsibility to inform the framework about the real state > > > > > of > > > > > the > > > > > lines and > > > > > synchronize it. > > > > > > > > > > Another case is when the firmware sets the line in non- > > > > > disabled > > > > > state > > > > > and > > > > > by some reason you need to disable it. The question is, why? > > > > > > > > Not getting this point... > > > > > > I understand that in your case "firmware" is what DTB provides. > > > So taking into account that the default of hardware is PU, it > > > needs > > > a mechanism to override that, correct? > > > > > > > Exactly... > > > > > > > > As a side note, this came to my attention during this > > > > > > patchset > > > > > > [1] > > > > > > (and, ofr OF, was tested with it). > > > > > > > > > > > > [1]: > > > > > > https://lore.kernel.org/linux-input/20220708093448.42617-5-nuno.sa@xxxxxxxxxx/ > > > > > > > > > > Since this provides a GPIO chip, correct?, it's > > > > > responsibility of > > > > > the > > > > > driver to > > > > > synchronize it, no? Basically if you really don't trust > > > > > firmware, > > > > > you > > > > > may > > > > > > > > What do you mean by synchronize? > > > > > > Full duplex sync, i.e. setting flag to PU for the pins that > > > should > > > stay PU:ed > > > and disabling bias for the ones, that want it to be disabled. (PD > > > accordingly) > > > > > > > > go via all GPIO lines and switch them to the known (in > > > > > software) > > > > > state. This > > > > > approach on the other hand is error prone, because firmware > > > > > should > > > > > know better > > > > > which pin is used for which purpose, no? If you don't trust > > > > > firwmare > > > > > (in some > > > > > cases), then it's a matter of buggy platform that has to be > > > > > quirked > > > > > out. > > > > > > > > I'm not getting what you mean by "firmware should know better"? > > > > So, > > > > basically, and let's take OF as example, you can request a GPIO > > > > in > > > > OF > > > > by doing something like: > > > > > > > > foo-gpios = <&gpio 1 GPIO_PULL_UP>; > > > > > > > > In this way, when the consumer driver gets the gpio, all the > > > > flags > > > > will > > > > be properly set so that when we set a direction (for example) > > > > the > > > > gpiochip's 'set_config()' will be called and the driver does > > > > what > > > > it > > > > needs to setup the pull-up. If we want BIAS_DISABLED on the > > > > pin, > > > > there's no way to the same as the above. So basically, this can > > > > ever > > > > happen: > > > > > > > > https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib.c#L2227 > > > > > > > > (only possible from the gpiochip cdev interface) > > > > > > > > So, what I'm proposing is to be possible to do from OF: > > > > > > > > foo-gpios = <&gpio 1 GPIO_PULL_DISABLE>; > > > > > > > > And then we will get into the gpiochip's 'set_config()' to > > > > disable > > > > the > > > > pull-up or pull-down. > > > > > > > > As I said, my device is an input keymap that can export pins as > > > > GPIOs > > > > (to be consumed by gpio_keys). The pins by default have pull- > > > > ups > > > > that > > > > can be disabled by doing a device i2c write. I'm just trying to > > > > use > > > > the > > > > infrastructure that already exists in gpiolib (for pull- > > > > up|down) to > > > > accomplish this. There's no pinctrl driver controlling the > > > > pins. > > > > The > > > > device itself controls them and having this device as a pinctrl > > > > one > > > > is > > > > not really applicable. > > > > > > Yes, I have got it eventually. The root cause is that after reset > > > you > > > have a > > > hardware that doesn't disable bias. > > > > > > Now, we have DT properties for PD and PU, correct? > > > For each requested pin you decide either to leave the state as it > > > is, > > > or > > > apply bias. > > > > > > in ->probe() of your GPIO you reset hardware and for each GPIO > > > descriptor you > > > set PU flag. > > > In ->request(), don;t know the name by heart, you disable BIAS > > > based > > > on absence > > > of flags, it can be done without an additional properties, purely > > > in > > > the GPIO > > > OF code. Do I understand this correctly? > > > > > > > Alright, I think now you got it and we are on the same page. If I > > understood your suggestion, users would just use GPIO_PULL_UP in > > dtb if > > wanting the default behavior. I would then use the gpiochip > > 'request()' > > callback to test the for pull-up flag right? > > Something like this, yes. > > > If I'm getting this right, there's a problem with it... > > gpiod_configure_flags() is called after gpiod_request() which means > > that the gpiod descriptor won't still have the BIAS flags set. And > > I > > don't think there's a way (at least clean and easy) to get the > > firmware > > lookup flags from the request callback? > > > > So, honestly the only option I see to do it without changing > > gpioblib > > would be to hook this change in output/input callbacks which is far > > from being optimal... > > > > So, in the end having this explicitly like this feels the best > > option > > to me. Sure, I can find some workaround in my driver but that does > > not > > change this... > > Ok, let me think about it. Meanwhile, maybe others have better ideas > already? > Sure, I'm still thinking that having this extra property and explicitly set it from OF is not that bad :) > > " > > git grep "PIN_CONFIG_BIAS_DISABLE" drivers/gpio/ > > Hint: `git grep -lw "PIN_CONFIG_BIAS_DISABLE" -- drivers/gpio` > nice.. > > drivers/gpio/gpio-aspeed.c:963: else if (param == > > PIN_CONFIG_BIAS_DISABLE || > > drivers/gpio/gpio-merrifield.c:197: if > > ((pinconf_to_config_param(config) == PIN_CONFIG_BIAS_DISABLE) || > > drivers/gpio/gpio-omap.c:903: case PIN_CONFIG_BIAS_DISABLE: > > drivers/gpio/gpio-pca953x.c:573: if (config == > > PIN_CONFIG_BIAS_DISABLE) > > drivers/gpio/gpio-pca953x.c:592: case > > PIN_CONFIG_BIAS_DISABLE: > > " > > > > AFAICT, the only way this path is possible for these drivers is > > through > > gpiolib cdev which might not be what the authors of the drivers > > were > > expecting... > > gpio-merrifield is bad example, it has a pin control. > gpio-pca953x as I said should effectively be a pin control driver. > > For the two left it might be the case. > Well the thing is that even if we have pinctrl like for example, gpio-omap, it is still true that there's no way to get into 'omap_gpio_set_config()' for 'PIN_CONFIG_BIAS_DISABLE' and call 'gpiochip_generic_config()'. (naturally in this case, one can directly use pinctrl properties to control the pin but still...) - Nuno Sá
