On Tue, Oct 21, 2025 at 02:06:30PM +0200, Bartosz Golaszewski wrote: > On Tue, Oct 21, 2025 at 3:53 AM Manivannan Sadhasivam <[email protected]> wrote: > > > > > > That only happens if the driver uses the reset API. If you go with the > > > GPIOLIB then none of this matters. I definitely don't want to change > > > the existing DT sources either but I want to find out if the code in > > > this series is suitable (with some modifications) for supporting the > > > PERST# line or if the logic behind it is more complex and possibly > > > requires separate, more fine-grained handling. > > > > > > > All PCI controllers relied on '{reset/perst}-gpios' property for handling > > the > > PERST# signal. Now if we change it to a reset line, then the drivers have to > > first detect it as a reset line and use the reset APIs, if not fallback to > > gpiod > > APIs (for DT backwards compatibility), which will add unncessary churn IMO. > > > > Ok so some platforms define perst-gpios while others use reset-gpios, > I see now. Yeah, it's better to go with explicit GPIOs then. > > > But if there is no way the GPIO subsystem is going to support shared GPIOs, > > then > > we have to live with it. > > > > Well, there is going to be. We already de-facto have it but it doesn't > work very well and is fragile (I'm talking about the non-exclusive > flag). I very much intend to bring this upstream. > > My question wrt PCI PERST# was whether this is useful for it because > IIRC all endpoints sharing the signal will assert it (or rather their > pwrctl drivers will) and then only deassert it once all endpoints are > powered up. This would translate to the pwrctl driver doing the > following for each endpoint: > > perst = gpiod_get(dev, "perst"); > gpiod_set_value_cansleep(perst, 1); > > Do the power up. > > gpiod_set_value_cansleep(perst, 0); > > And with the implementation this series proposes it would mean that > the perst signal will go high after the first endpoint pwrctl driver > sets it to high and only go down once the last driver sets it to low. > The only thing I'm not sure about is the synchronization between the > endpoints - how do we wait for all of them to be powered-up before > calling the last gpiod_set_value()? >
That will be handled by the pwrctrl core. Not today, but in the coming days. - Mani -- மணிவண்ணன் சதாசிவம்
