Re: [PATCH v2] treewide, serdev: change receive_buf() return type to size_t

[Alex Elder <elder@ieee.org>]

On 1/22/24 12:05 PM, Francesco Dolcini wrote:
> From: Francesco Dolcini <francesco.dolcini@toradex.com>
> 
> receive_buf() is called from ttyport_receive_buf() that expects values
> ">= 0" from serdev_controller_receive_buf(), change its return type from
> ssize_t to size_t.
> 
> The need for this clean-up was noticed while fixing a warning, see
> commit 94d053942544 ("Bluetooth: btnxpuart: fix recv_buf() return value").
> Changing the callback prototype to return an unsigned seems the best way
> to document the API and ensure that is properly used.
> 
> GNSS drivers implementation of serdev receive_buf() callback return
> directly the return value of gnss_insert_raw(). gnss_insert_raw()
> returns a signed int, however this is not an issue since the value
> returned is always positive, because of the kfifo_in() implementation.

Agreed.

> gnss_insert_raw() could be changed to return also an unsigned, however
> this is not implemented here as request by the GNSS maintainer Johan
> Hovold.

I was going to suggest this, and suggest changing the "ret" in
gnss_insert_raw() to return size_t.  But to really do that right
it would include some other changes as well.  Leaving it as an
int as Johan suggests preserves correct behavior.

One minor point below, plus a couple comments affirming that
an int return value is OK because it's always non-negative.

Reviewed-by: Alex Elder <elder@linaro.org>


> Suggested-by: Jiri Slaby <jirislaby@kernel.org>
> Link: https://lore.kernel.org/all/087be419-ec6b-47ad-851a-5e1e3ea5cfcc@kernel.org/
> Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> #for-iio
> ---
> v1:
>   - https://lore.kernel.org/all/20231214170146.641783-1-francesco@dolcini.it/
> v2:
>   - rebased on 6.8-rc1
>   - add acked-by Jonathan
>   - do not change gnss_insert_raw()
>   - do not change the code style of the gnss code
>   - commit message improvements, explain the reasons for doing only minimal
>     changes on the GNSS part
> ---
>   drivers/bluetooth/btmtkuart.c              |  4 ++--
>   drivers/bluetooth/btnxpuart.c              |  4 ++--
>   drivers/bluetooth/hci_serdev.c             |  4 ++--
>   drivers/gnss/serial.c                      |  2 +-
>   drivers/gnss/sirf.c                        |  2 +-
>   drivers/greybus/gb-beagleplay.c            |  6 +++---
>   drivers/iio/chemical/pms7003.c             |  4 ++--
>   drivers/iio/chemical/scd30_serial.c        |  4 ++--
>   drivers/iio/chemical/sps30_serial.c        |  4 ++--
>   drivers/iio/imu/bno055/bno055_ser_core.c   |  4 ++--
>   drivers/mfd/rave-sp.c                      |  4 ++--
>   drivers/net/ethernet/qualcomm/qca_uart.c   |  2 +-
>   drivers/nfc/pn533/uart.c                   |  4 ++--
>   drivers/nfc/s3fwrn5/uart.c                 |  4 ++--
>   drivers/platform/chrome/cros_ec_uart.c     |  4 ++--
>   drivers/platform/surface/aggregator/core.c |  4 ++--
>   drivers/tty/serdev/serdev-ttyport.c        | 10 ++++------
>   include/linux/serdev.h                     |  8 ++++----
>   sound/drivers/serial-generic.c             |  4 ++--
>   19 files changed, 40 insertions(+), 42 deletions(-)
> 

. . .

> diff --git a/drivers/mfd/rave-sp.c b/drivers/mfd/rave-sp.c
> index 6ff84b2600c5..62a6613fb070 100644
> --- a/drivers/mfd/rave-sp.c
> +++ b/drivers/mfd/rave-sp.c
> @@ -471,8 +471,8 @@ static void rave_sp_receive_frame(struct rave_sp *sp,
>   		rave_sp_receive_reply(sp, data, length);
>   }
>   
> -static ssize_t rave_sp_receive_buf(struct serdev_device *serdev,
> -				   const u8 *buf, size_t size)
> +static size_t rave_sp_receive_buf(struct serdev_device *serdev,
> +				  const u8 *buf, size_t size)
>   {
>   	struct device *dev = &serdev->dev;
>   	struct rave_sp *sp = dev_get_drvdata(dev);

One return path in this function returns (src - buf), which is
*almost* guaranteed to be positive.  The one case it wouldn't
be is if the assignment of end wraps around, and that's not
checked.

I think it's fine, but... That seems theoretically possible.


> diff --git a/drivers/net/ethernet/qualcomm/qca_uart.c b/drivers/net/ethernet/qualcomm/qca_uart.c
> index 223321897b96..20f50bde82ac 100644

. . .

> diff --git a/drivers/platform/surface/aggregator/core.c b/drivers/platform/surface/aggregator/core.c
> index 9591a28bc38a..ba550eaa06fc 100644
> --- a/drivers/platform/surface/aggregator/core.c
> +++ b/drivers/platform/surface/aggregator/core.c
> @@ -227,8 +227,8 @@ EXPORT_SYMBOL_GPL(ssam_client_bind);
>   
>   /* -- Glue layer (serdev_device -> ssam_controller). ------------------------ */
>   
> -static ssize_t ssam_receive_buf(struct serdev_device *dev, const u8 *buf,
> -				size_t n)
> +static size_t ssam_receive_buf(struct serdev_device *dev, const u8 *buf,
> +			       size_t n)
>   {
>   	struct ssam_controller *ctrl;
>   	int ret;

Here you the return value will be positive despite ret being
a signed int.  So like the GNSS case, this is OK.

> diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c
> index e94e090cf0a1..3d7ae7fa5018 100644

. . .

> diff --git a/sound/drivers/serial-generic.c b/sound/drivers/serial-generic.c
> index d6e5aafd697c..36409a56c675 100644
> --- a/sound/drivers/serial-generic.c
> +++ b/sound/drivers/serial-generic.c
> @@ -100,8 +100,8 @@ static void snd_serial_generic_write_wakeup(struct serdev_device *serdev)
>   	snd_serial_generic_tx_wakeup(drvdata);
>   }
>   
> -static ssize_t snd_serial_generic_receive_buf(struct serdev_device *serdev,
> -					      const u8 *buf, size_t count)
> +static size_t snd_serial_generic_receive_buf(struct serdev_device *serdev,
> +					     const u8 *buf, size_t count)
>   {
>   	int ret;
>   	struct snd_serial_generic *drvdata = serdev_device_get_drvdata(serdev);

Same thing here.