On Wed, Jan 31, 2024 at 9:57 AM Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > Hi Krzysztof, > > something is odd with the addresses on this patch, because neither GPIO > maintainer is on CC nor linux-gpio@vger, and it's such a GPIO-related > patch. We only saw it through side effects making <linux/gpio/driver.h> > optional, as required by this patch. > > Please also CC Geert Uytterhoeven, the author of the GPIO aggregator. > > i.e. this: > > 2. !GPIOLIB stub: > > https://lore.kernel.org/all/20240125081601.118051-3-krzysztof.kozlowski@xxxxxxxxxx/ > > On Mon, Jan 29, 2024 at 12:53 PM Krzysztof Kozlowski > <krzysztof.kozlowski@xxxxxxxxxx> wrote: > > > Devices sharing a reset GPIO could use the reset framework for > > coordinated handling of that shared GPIO line. We have several cases of > > such needs, at least for Devicetree-based platforms. > > > > If Devicetree-based device requests a reset line, while "resets" > > Devicetree property is missing but there is a "reset-gpios" one, > > instantiate a new "reset-gpio" platform device which will handle such > > reset line. This allows seamless handling of such shared reset-gpios > > without need of changing Devicetree binding [1]. > > > > To avoid creating multiple "reset-gpio" platform devices, store the > > Devicetree "reset-gpios" GPIO specifiers used for new devices on a > > linked list. Later such Devicetree GPIO specifier (phandle to GPIO > > controller, GPIO number and GPIO flags) is used to check if reset > > controller for given GPIO was already registered. > > > > If two devices have conflicting "reset-gpios" property, e.g. with > > different ACTIVE_xxx flags, this would allow to spawn two separate > > "reset-gpio" devices, where the second would fail probing on busy GPIO > > request. > > > > Link: https://lore.kernel.org/all/YXi5CUCEi7YmNxXM@xxxxxxxxxxxxxxxxxx/ [1] > > Cc: Bartosz Golaszewski <brgl@xxxxxxxx> > > Cc: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx> > > Cc: Sean Anderson <sean.anderson@xxxxxxxx> > > Reviewed-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> > (...) > > In my naive view, this implements the following: > > reset -> virtual "gpio" -> many physical gpios[0..n] This is a different problem: it supports many users enabling the same GPIO (in Krzysztof's patch it's one but could be more if needed) but - unlike the broken NONEXCLUSIVE GPIOs in GPIOLIB - it counts the number of users and doesn't disable the GPIO for as long as there's at least one. Bart > > So if there was already a way in the kernel to map one GPIO to > many GPIOs, the framework could just use that with a simple > single GPIO? > > See the bindings in: > Documentation/devicetree/bindings/gpio/gpio-delay.yaml > > This is handled by drivers/gpio/gpio-aggregator.c. > > This supports a 1-to-1 map: one GPIO in, one GPIO out, same offset. > So if that is extended to support 1-to-many, this problem is solved. > > Proposed solution: add a single boolean property such as > aggregate-all-gpios; to the gpio-delay node, making it provide > one single gpio at offset 0 on the consumer side, and refuse any > more consumers. > > This will also solve the problem with induced delays on > some GPIO lines as I can see was discussed in the bindings, > the gpio aggregator already supports that, but it would work > fine with a delay being zero as well. > > This avoids all the hackery with driver stubs etc as well. > > Yours, > Linus Walleij
