Re: [PATCH v2 4/4] serial: qcom_geni: Use devm_krealloc_array

James Clark
2023-03-20T10:03:42Z

On 18/03/2023 17:34, Jonathan Cameron wrote:
> On Fri, 17 Mar 2023 11:34:49 +0000
> James Clark <james.clark@arm.com> wrote:
>
>> On 11/03/2023 19:18, Jonathan Cameron wrote:
>>> On Thu, 9 Mar 2023 15:03:33 +0000
>>> James Clark <james.clark@arm.com> wrote:
>>>
>>>> Now that it exists, use it instead of doing the multiplication manually.
>>>>
>>>> Signed-off-by: James Clark <james.clark@arm.com>
>>>
>>> Hmm. I've stared at the users of this for a bit, and it's not actually obvious
>>> that it's being used as an array of u32. The only typed user of this is as
>>> the 2nd parameter of
>>> tty_insert_flip_string() which is an unsigned char *
>>>
>>> I wonder if that sizeof(u32) isn't a 'correct' description of where the 4 is coming
>>> from even if it has the right value? Perhaps the fifo depth is just a multiple of 4?
>>>
>>> Jonathan
>>>
>>
>> The commit that added it (b8caf69a6946) seems to hint that something
>> reads from it in words. And I see this:
>>
>> /* We always configure 4 bytes per FIFO word */
>> #define BYTES_PER_FIFO_WORD 4U
>>
>> Perhaps sizeof(u32) isn't as accurate of a description as using
>> BYTES_PER_FIFO_WORD but I'd be reluctant to make a change because I
>> don't really understand the implications.
>
> Agreed with your analysis. + fully understand why you don't want to change
> it.
>
> I'd be tempted to take the view that whilst it's allocated in 4 byte chunks
> because it's accessed elsewhere as a set of 1 byte entries, krealloc_array
> isn't appropriate and so just leave it with devm_krealloc()
>
> Risk is that a steady stream of patches will turn up 'fixing' this as
> it will be easy for people to find with a script. Maybe better to just add
> a comment (either with or without your patch).

Ok that makes sense to me. I can add a comment instead this patch to
change this one.

>>
>> There is also this in handle_rx_console():
>>
>> unsigned char buf[sizeof(u32)];
>>
>> James
>>
>>>
>>>
>>>> ---
>>>> drivers/tty/serial/qcom_geni_serial.c | 6 +++---
>>>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
>>>> index d69592e5e2ec..23fc33d182ac 100644
>>>> --- a/drivers/tty/serial/qcom_geni_serial.c
>>>> +++ b/drivers/tty/serial/qcom_geni_serial.c
>>>> @@ -1056,9 +1056,9 @@ static int setup_fifos(struct qcom_geni_serial_port *port)
>>>> (port->tx_fifo_depth * port->tx_fifo_width) / BITS_PER_BYTE;
>>>>
>>>> if (port->rx_buf && (old_rx_fifo_depth != port->rx_fifo_depth) && port->rx_fifo_depth) {
>>>> - port->rx_buf = devm_krealloc(uport->dev, port->rx_buf,
>>>> - port->rx_fifo_depth * sizeof(u32),
>>>> - GFP_KERNEL);
>>>> + port->rx_buf = devm_krealloc_array(uport->dev, port->rx_buf,
>>>> + port->rx_fifo_depth, sizeof(u32),
>>>> + GFP_KERNEL);
>>>> if (!port->rx_buf)
>>>> return -ENOMEM;
>>>> }
>>>
>