On Tue, Sep 21, 2021 at 6:40 AM Andrew Jeffery <andrew@xxxxxxxx> wrote: > The devicetree binding allows specifying which pins are GPIO vs LED. > Limiting the instantiated gpiochip to just these pins as the driver > currently does requires an arbitrary mapping between pins and GPIOs, but > such a mapping is not implemented by the driver. As a result, > specifying GPIOs in such a way that they don't map 1-to-1 to pin indexes > does not function as expected. > > Establishing such a mapping is more complex than not and even if we did, > doing so leads to a slightly hairy userspace experience as the behaviour > of the PCA955x gpiochip would depend on how the pins are assigned in the > devicetree. Instead, always expose all pins via the gpiochip to provide > a stable interface and track which pins are in use. > > Specifying a pin as `type = <PCA955X_TYPE_GPIO>;` in the devicetree > becomes a no-op. > > I've assessed the impact of this change by looking through all of the > affected devicetrees as of the tag leds-5.15-rc1: > > ``` > $ git grep -l 'pca955[0123]' $(find . -name dts -type d) > arch/arm/boot/dts/aspeed-bmc-ibm-everest.dts > arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts > arch/arm/boot/dts/aspeed-bmc-opp-mihawk.dts > arch/arm/boot/dts/aspeed-bmc-opp-mowgli.dts > arch/arm/boot/dts/aspeed-bmc-opp-swift.dts > arch/arm/boot/dts/aspeed-bmc-opp-tacoma.dts > arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts > ``` > > These are all IBM-associated platforms. I've analysed both the > devicetrees and schematics where necessary to determine whether any > systems hit the hazard of the current broken behaviour. For the most > part, the systems specify the pins as either all LEDs or all GPIOs, or > at least do so in a way such that the broken behaviour isn't exposed. > > The main counter-point to this observation is the Everest system whose > devicetree describes a large number of PCA955x devices and in some cases > has pin assignments that hit the hazard. However, there does not seem to > be any use of the affected GPIOs in the userspace associated with > Everest. > > Regardless, any use of the hazardous GPIOs in Everest is already broken, > so let's fix the interface and then fix any already broken userspace > with it. > > Signed-off-by: Andrew Jeffery <andrew@xxxxxxxx> Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx> Yours, Linus Walleij
