Re: [PATCH] gpio: Revert regression in sysfs-gpio (gpiolib.c)

[Michael Walle <michael@walle.cc>]

[+ Saravana ]

Am 2022-03-15 16:32, schrieb Bartosz Golaszewski:
> On Mon, Mar 14, 2022 at 4:55 PM Michael Walle <michael@walle.cc> wrote:
>> > Some GPIO lines have stopped working after the patch
>> > commit 2ab73c6d8323f ("gpio: Support GPIO controllers without pin-ranges")
>> >
>> > And this has supposedly been fixed in the following patches
>> > commit 89ad556b7f96a ("gpio: Avoid using pin ranges with !PINCTRL")
>> > commit 6dbbf84603961 ("gpiolib: Don't free if pin ranges are not defined")
>> >
>> > But an erratic behavior where some GPIO lines work while others do not work
>> > has been introduced.
>> >
>> > This patch reverts those changes so that the sysfs-gpio interface works
>> > properly again.
>> >
>> > Signed-off-by: Marcelo Roberto Jimenez <marcelo.jimenez@gmail.com>
>> 
>> This breaks the pinctrl-microchip-sgpio driver as far as I can see.
>> 
>> I tried to debug it and this is what I have discovered so far:
>>  (1) the sgpio driver will use the gpio_stub_drv for its child nodes.
>>      Looks like a workaround, see [1].
>>  (2) these will have an empty gpio range
>>  (3) with the changes of this patch, pinctrl_gpio_request() will now
>>      be called and will fail with -EPROBE_DEFER.
>> 
>> I'm not exactly sure what to do here. Saravana Kannan once suggested
>> to use devm_of_platform_populate() to probe the child nodes [2]. But
>> I haven't found any other driver doing that.

Oh I meant gpio/pinctrl drivers.

> TI AEMIF driver (drivers/memory/ti-aemif.c) does something like this:
> 
> 406         if (np) {
> 407                 for_each_available_child_of_node(np, child_np) {
> 408                         ret = of_platform_populate(child_np, NULL,
> 409                                                    dev_lookup, 
> dev);
> 410                         if (ret < 0) {
> 411                                 of_node_put(child_np);
> 412                                 goto error;
> 413                         }
> 414                 }
> 415         } else if (pdata) {
> 416                 for (i = 0; i < pdata->num_sub_devices; i++) {
> 417                         pdata->sub_devices[i].dev.parent = dev;
> 418                         ret =
> platform_device_register(&pdata->sub_devices[i]);
> 419                         if (ret) {
> 420                                 dev_warn(dev, "Error register sub
> device %s\n",
> 421                                          
> pdata->sub_devices[i].name);
> 422                         }
> 423                 }
> 424         }
> 
> A bunch of different devices (like NAND) get instantiated this way.
> Would this work?

I started to try this out, but then I was wondering if there weren't
other gpio/pinctrl drivers with the same problem. And judging by the
reports [1], I'd say there are. Then I wasn't sure if this is actually
the correct fix here - or if that old workaround [2] doesn't work
anymore because it might have that empty ranges "feature".

To answer your question: I don't know. But I don't know if that is
actually the correct way of fixing this either.

>> Also, I'm not sure if there are any other other driver which get
>> broken by this. I.e. ones falling into the gpio_stub_drv category.
>> 
>> [1] 
>> https://lore.kernel.org/lkml/20210122193600.1415639-1-saravanak@google.com/
>> [2] 
>> https://lore.kernel.org/lkml/CAGETcx9PiX==mLxB9PO8Myyk6u2vhPVwTMsA5NkD-ywH5xhusw@mail.gmail.com/
>> 
>> -michael
>> 
>> NB. this patch doesn't contain a Fixes tag. Was this on purpose?

-michael

[1] https://lore.kernel.org/lkml/20220314192522.GA3031157@roeck-us.net/
[2] 
https://lore.kernel.org/lkml/20210122193600.1415639-1-saravanak@google.com/