Message-ID: <25b5fb44-fc33-cc2d-5a36-64e780015824@arm.com>
Date:   Mon, 20 Mar 2023 10:03:06 +0000
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Subject: Re: [PATCH v2 4/4] serial: qcom_geni: Use devm_krealloc_array
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To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        linux-kernel@vger.kernel.org, linux@roeck-us.net,
        michal.simek@amd.com, Jonathan Corbet <corbet@lwn.net>,
        Jean Delvare <jdelvare@suse.com>,
        Anand Ashok Dumbre <anand.ashok.dumbre@xilinx.com>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Michal Simek <michal.simek@xilinx.com>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Konrad Dybcio <konrad.dybcio@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>, linux-doc@vger.kernel.org,
        linux-hwmon@vger.kernel.org, linux-iio@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-arm-msm@vger.kernel.org, linux-serial@vger.kernel.org
References: <20230309150334.216760-1-james.clark@arm.com>
 <20230309150334.216760-5-james.clark@arm.com>
 <20230311191800.74ec2b84@jic23-huawei>
 <74d8b579-6ea8-d6f3-170f-ea13534b4565@arm.com>
 <20230318173402.20a4f60d@jic23-huawei>
From:   James Clark <james.clark@arm.com>
In-Reply-To: <20230318173402.20a4f60d@jic23-huawei>
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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;
>>>>  	}  
>>>   
>