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

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Message-ID: <b9ea7e0e-7dd1-460b-950a-083620dd52e9@wanadoo.fr>
Date: Wed, 11 Jun 2025 00:48:09 +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 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.

> Can you confirm that you really want the result to be checked here?

That's the point of those new gpio setters, isn't it? If we do not check the
result, I do not understand the purpose of the migration.

Yours sincerely,
Vincent Mailhol