linux-kernel - Re: [PATCH 3/4] net: can: mcp251x: use new GPIO line value setter callbacks

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Message-ID: <CAMRc=Mf4qupdJEm9mWPF3-B3hprn6AvP7Po2=aQYbaSvFf8OeA@mail.gmail.com>
Date: Tue, 10 Jun 2025 18:05:55 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mediatek@...ts.infradead.org, linux-can@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, Andrew Lunn <andrew@...n.ch>, 
	Vladimir Oltean <olteanv@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Linus Walleij <linus.walleij@...aro.org>, "Chester A. Unal" <chester.a.unal@...nc9.com>, 
	Daniel Golle <daniel@...rotopia.org>, DENG Qingfang <dqfext@...il.com>, 
	Sean Wang <sean.wang@...iatek.com>, Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
	Marc Kleine-Budde <mkl@...gutronix.de>, Heiner Kallweit <hkallweit1@...il.com>, 
	Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH 3/4] net: can: mcp251x: use new GPIO line value setter callbacks

On Tue, Jun 10, 2025 at 5:48 PM Vincent Mailhol
<mailhol.vincent@...adoo.fr> wrote:
>
> On 10/06/2025 at 23:05, Bartosz Golaszewski wrote:
> > On Tue, Jun 10, 2025 at 3:55 PM Vincent Mailhol
> > <mailhol.vincent@...adoo.fr> wrote:
> >>
> >> On 10/06/2025 at 21:37, Bartosz Golaszewski wrote:
> >>> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >>>
> >>> struct gpio_chip now has callbacks for setting line values that return
> >>> an integer, allowing to indicate failures. Convert the driver to using
> >>> them.
> >>>
> >>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >>                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >>
> >> This does not match the address with which you sent the patch: brgl@...ev.pl
> >>
> >>> ---
> >>>  drivers/net/can/spi/mcp251x.c | 16 ++++++++++------
> >>>  1 file changed, 10 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/drivers/net/can/spi/mcp251x.c b/drivers/net/can/spi/mcp251x.c
> >>> index ec5c64006a16f703bc816983765584c5f3ac76e8..7545497d14b46c6388f3976c2bf7b9a99e959c1e 100644
> >>> --- a/drivers/net/can/spi/mcp251x.c
> >>> +++ b/drivers/net/can/spi/mcp251x.c
> >>> @@ -530,8 +530,8 @@ static int mcp251x_gpio_get_multiple(struct gpio_chip *chip,
> >>>       return 0;
> >>>  }
> >>>
> >>> -static void mcp251x_gpio_set(struct gpio_chip *chip, unsigned int offset,
> >>> -                          int value)
> >>> +static int mcp251x_gpio_set(struct gpio_chip *chip, unsigned int offset,
> >>> +                         int value)
> >>>  {
> >>>       struct mcp251x_priv *priv = gpiochip_get_data(chip);
> >>>       u8 mask, val;
> >>> @@ -545,9 +545,11 @@ static void mcp251x_gpio_set(struct gpio_chip *chip, unsigned int offset,
> >>>
> >>>       priv->reg_bfpctrl &= ~mask;
> >>>       priv->reg_bfpctrl |= val;
> >>> +
> >>> +     return 0;
> >>
> >> mcp251x_gpio_set() calls mcp251x_write_bits() which calls mcp251x_spi_write()
> >> which can fail.
> >>
> >> For this change to really make sense, the return value of mcp251x_spi_write()
> >> should be propagated all the way around.
> >>
> >
> > I don't know this code so I followed the example of the rest of the
> > codebase where the result of this function is never checked - even in
> > functions that do return values. I didn't know the reason for this and
> > so didn't want to break anything as I have no means of testing it.
>
> The return value of mcp251x_spi_write() is used in mcp251x_hw_reset(). In other
> locations, mcp251x_spi_write() is only used in functions which return void, so
> obviously, the return value is not checked.
>

Wait, after a second look GPIO callbacks (including those that return
a value like request()) use mcp251x_write_bits() which has no return
value. It probably should propagate what mcp251x_spi_write() returns
but that's material for a different series. The goal of this one is to
use the new setters treewide and drop the old ones from struct
gpio_chip.

Bart