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. > 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
