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? 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... " git grep "PIN_CONFIG_BIAS_DISABLE" drivers/gpio/ 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... - Nuno Sá
