On Thu, Jul 14, 2022 at 09:14:21AM +0200, Nuno Sá wrote: > On Thu, 2022-07-14 at 12:20 +0800, Kent Gibson wrote: > > On Wed, Jul 13, 2022 at 08:36:38PM +0300, Andy Shevchenko wrote: > > > On Wed, Jul 13, 2022 at 03:14:18PM +0200, Nuno Sá wrote: > > > > This change prepares the gpio core to look at firmware flags and > > > > set > > > > 'FLAG_BIAS_DISABLE' if necessary. It works in similar way to > > > > 'GPIO_PULL_DOWN' and 'GPIO_PULL_UP'. > > > > > > ... > > > > > > > GPIO_PULL_UP = (1 << 4), > > > > GPIO_PULL_DOWN = (1 << 5), > > > > + GPIO_PULL_DISABLE = (1 << 6), > > > > > > To me it seems superfluous. You have already two flags: > > > PUp > > > PDown > > > When none is set --> Pdisable > > > > > > > Agree with Andy on this. The FLAG_BIAS_DISABLE was added, by me, to > > allow the cdev interface to support bias. cdev requires a "don't > > care" > > state, distinct from an explicit BIAS_DISABLE. > > The FLAG_BIAS_DISABLE allows gpiolib-cdev to communicate that to > > gpiolib, without altering the interpretation of the existing PULL_UP > > and > > PULL_DOWN flags. > > That is not an issue on the machine interface, where the two > > GPIO_PULL > > flags suffice. > > > > I see, but this means we can only disable the pin BIAS through > userspace. I might be wrong but I don't see a reason why it wouldn't be > valid to do it from an in kernel path as we do for PULL-UPS and PULL- > DOWNS > > > If you are looking for the place where FLAG_BIAS_DISABLE is set it is > > in > > gpio_v2_line_config_flags_to_desc_flags() in gpiolib-cdev.c. > > > > Referring to gpio_set_bias(), the only place in gpiolib the > > FLAG_BIAS_DISABLE is used, if neither FLAG_PULL_UP, FLAG_PULL_DOWN, > > nor FLAG_BIAS_DISABLE are set then the bias configuration remains > > unchanged (the don't care case) - no change is passed to the driver. > > Otherwise the corresponding PIN_CONFIG_BIAS flag is passed to the > > driver. > > > > Exactly, but note FLAG_BIAS_DISABLE can only be set from userspace at > this point (IIUTC). If everyone agrees that should be case, so be it. > But as I said, I just don't see why it's wrong to do it within the > kernel. > Believe it or not gpiolib-cdev is part of the kernel, not userspace - it just provides an interface to userspace. Bias can be disabled by calling gpiod_direction_input() or gpiod_direction_output() after setting the FLAG_BIAS_DISABLE, as gpiolib-cdev does. Does that work for you? Cheers, Kent. > > If there are cases of drivers not fully or correctly supporting those > > PIN_CONFIG_BIAS flags, then that is an issue with those drivers. > > > > Look at my reply to Andy in the cover for more details > > - Nuno Sá
