linux-kernel - Re: [PATCH] gpio: mmio: do not calculate bgpio

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Date: Wed, 26 Jun 2024 14:06:27 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: Shiji Yang <yangshiji66@...look.com>
Cc: linux-gpio@...r.kernel.org, Bartosz Golaszewski <brgl@...ev.pl>, 
	Asmaa Mnebhi <asmaa@...dia.com>, Andy Shevchenko <andy.shevchenko@...il.com>, 
	linux-kernel@...r.kernel.org, Mark Mentovai <mark@...tovai.com>, 
	Jonas Gorski <jonas.gorski@...il.com>, Lóránd Horváth <lorand.horvath82@...il.com>
Subject: Re: [PATCH] gpio: mmio: do not calculate bgpio_bits via "ngpios"

Hi Shiji,

thanks for your patch!

On Tue, Jun 25, 2024 at 3:22 AM Shiji Yang <yangshiji66@...look.com> wrote:

> bgpio_bits must be aligned with the data bus width. For example, on a
> 32 bit big endian system and we only have 16 GPIOs. If we only assume
> bgpio_bits=16 we can never control the GPIO because the base address
> is the lowest address.
>
> low address                          high address
> -------------------------------------------------
> |   byte3   |   byte2   |   byte1   |   byte0   |
> -------------------------------------------------
> |    NaN    |    NaN    |  gpio8-15 |  gpio0-7  |
> -------------------------------------------------
>
> Fixes: 55b2395e4e92 ("gpio: mmio: handle "ngpios" properly in bgpio_init()")
> Fixes: https://github.com/openwrt/openwrt/issues/15739
> Reported-by: Mark Mentovai <mark@...tovai.com>
> Signed-off-by: Shiji Yang <yangshiji66@...look.com>
> Suggested-By: Mark Mentovai <mark@...tovai.com>
> Reviewed-by: Jonas Gorski <jonas.gorski@...il.com>
> Tested-by: Lóránd Horváth <lorand.horvath82@...il.com>

Commit  55b2395e4e92 also contains this:

@@ -614,10 +616,15 @@ int bgpio_init(struct gpio_chip *gc, struct device *dev,
        gc->parent = dev;
        gc->label = dev_name(dev);
        gc->base = -1;
-       gc->ngpio = gc->bgpio_bits;
        gc->request = bgpio_request;

After this patch gc->ngpio will be unset for any GPIO chip that
provides a ngpios property, so restore the above line too.

But maybe a better fix is:

+ #include <linux/types.h>
(...)
+  else
+               gc->bgpio_bits = round_up(gc->ngpio, sizeof(phys_addr_t) * 8);

?

Yours,
Linus Walleij