On Wed, Sep 24, 2025 at 11:25:12AM -0700, Dmitry Torokhov wrote: > Hi Bartosz, > > On Wed, Sep 24, 2025 at 04:51:28PM +0200, Bartosz Golaszewski wrote: > > Here's a functional RFC for improving the handling of shared GPIOs in > > linux. > > > > Problem statement: GPIOs are implemented as a strictly exclusive > > resource in the kernel but there are lots of platforms on which single > > pin is shared by multiple devices which don't communicate so need some > > way of properly sharing access to a GPIO. What we have now is the > > GPIOD_FLAGS_BIT_NONEXCLUSIVE flag which was introduced as a hack and > > doesn't do any locking or arbitration of access - it literally just hand > > the same GPIO descriptor to all interested users. > > > > The proposed solution is composed of three major parts: the high-level, > > shared GPIO proxy driver that arbitrates access to the shared pin and > > exposes a regular GPIO chip interface to consumers, a low-level shared > > GPIOLIB module that scans firmware nodes and creates auxiliary devices > > that attach to the proxy driver and finally a set of core GPIOLIB > > changes that plug the former into the GPIO lookup path. > > > > The changes are implemented in a way that allows to seamlessly compile > > out any code related to sharing GPIOs for systems that don't need it. > > > > The practical use-case for this are the powerdown GPIOs shared by > > speakers on Qualcomm db845c platform, however I have also extensively > > tested it using gpio-virtuser on arm64 qemu with various DT > > configurations. > > How is this different from the existing gpio-backed regulator/supply? > IMO GPIOs are naturally exclusive-use resources (in cases when you need > to control them, not simply read their state), and when there is a need > to share them there are more appropriate abstractions that are built on > top of GPIOs... >
Not always... For something like shared reset line, consumers request the line as GPIO and expect gpiolib to do resource manangement. - Mani -- மணிவண்ணன் சதாசிவம்
