Messages in this thread | | | From | Linus Walleij <> | Date | Wed, 31 Jan 2024 09:57:00 +0100 | Subject | Re: [PATCH v6 4/6] reset: Instantiate reset GPIO controller for shared reset-gpios |
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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@linaro.org/
On Mon, Jan 29, 2024 at 12:53 PM Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> 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@robh.at.kernel.org/ [1] > Cc: Bartosz Golaszewski <brgl@bgdev.pl> > Cc: Chris Packham <chris.packham@alliedtelesis.co.nz> > Cc: Sean Anderson <sean.anderson@seco.com> > Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de> > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> (...)
In my naive view, this implements the following:
reset -> virtual "gpio" -> many physical gpios[0..n]
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
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