On Wed, Jan 31, 2024 at 9:57 AM Linus Walleij linus.walleij@linaro.org 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:
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]
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