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

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Message-ID: <e252f15f-ea80-4969-b754-82da5f9a7f56@wanadoo.fr>
Date: Wed, 11 Jun 2025 22:16:52 +0900
From: Vincent Mailhol <mailhol.vincent@...adoo.fr>
To: Bartosz Golaszewski <brgl@...ev.pl>
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 11/06/2025 at 01:05, Bartosz Golaszewski wrote:
> 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.

Yes. Read again my first message:

  mcp251x_gpio_set() calls mcp251x_write_bits() which calls mcp251x_spi_write()
  which can fail.

My point is that the grand father can fail.

> It probably should propagate what mcp251x_spi_write() returns

Exactly what I asked for :)

> but that's material for a different series.

Why? Are you going to do this other series?

If the answer is no, then please just do it here. Propagating the error in
mcp251x_write_bits() is a three line change. Am I asking for too much?

> The goal of this one is to
> use the new setters treewide and drop the old ones from struct
> gpio_chip.

Yours sincerely,
Vincent Mailhol