linux-kernel - Re: [PATCH v4 2/2] media: Add a driver for the ov7251 camera sensor

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Date:   Thu, 26 Apr 2018 15:40:31 +0300
From:   Todor Tomov <todor.tomov@...aro.org>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     mchehab@...nel.org, hverkuil@...all.nl,
        laurent.pinchart@...asonboard.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] media: Add a driver for the ov7251 camera sensor

On 26.04.2018 15:04, Sakari Ailus wrote:
> On Thu, Apr 26, 2018 at 10:16:56AM +0300, Sakari Ailus wrote:
>> On Thu, Apr 26, 2018 at 10:04:25AM +0300, Todor Tomov wrote:
>>> Hi Sakari,
>>>
>>> On 26.04.2018 09:50, Sakari Ailus wrote:
>>>> Hi Todor,
>>>>
>>>> On Wed, Apr 25, 2018 at 07:20:46PM +0300, Todor Tomov wrote:
>>>> ...
>>>>> +static int ov7251_write_reg(struct ov7251 *ov7251, u16 reg, u8 val)
>>>>> +{
>>>>> +	u8 regbuf[3];
>>>>> +	int ret;
>>>>> +
>>>>> +	regbuf[0] = reg >> 8;
>>>>> +	regbuf[1] = reg & 0xff;
>>>>> +	regbuf[2] = val;
>>>>> +
>>>>> +	ret = i2c_master_send(ov7251->i2c_client, regbuf, 3);
>>>>> +	if (ret < 0) {
>>>>> +		dev_err(ov7251->dev, "%s: write reg error %d: reg=%x, val=%x\n",
>>>>> +			__func__, ret, reg, val);
>>>>> +		return ret;
>>>>> +	}
>>>>> +
>>>>> +	return 0;
>>>>
>>>> How about:
>>>>
>>>> 	return ov7251_write_seq_regs(ov7251, reg, &val, 1);
>>>>
>>>> And put the function below ov2751_write_seq_regs().
>>>
>>> I'm not sure... It will calculate message length each time and then check
>>> that it is not greater than 5, which it is. Seems redundant.
>>>
>>>>
>>>>> +}
>>>>> +
>>>>> +static int ov7251_write_seq_regs(struct ov7251 *ov7251, u16 reg, u8 *val,
>>>>> +				 u8 num)
>>>>> +{
>>>>> +	const u8 maxregbuf = 5;
>>>>> +	u8 regbuf[maxregbuf];
> 
> Apparently this leads to bad positive sparse warning. I'd fix it by:
> 
> diff --git a/drivers/media/i2c/ov7251.c b/drivers/media/i2c/ov7251.c
> index 3e2c0c03dfa9..d3ebb7529fca 100644
> --- a/drivers/media/i2c/ov7251.c
> +++ b/drivers/media/i2c/ov7251.c
> @@ -643,12 +643,11 @@ static int ov7251_write_reg(struct ov7251 *ov7251, u16 reg, u8 val)
>  static int ov7251_write_seq_regs(struct ov7251 *ov7251, u16 reg, u8 *val,
>                                  u8 num)
>  {
> -       const u8 maxregbuf = 5;
> -       u8 regbuf[maxregbuf];
> +       u8 regbuf[5];
>         u8 nregbuf = sizeof(reg) + num * sizeof(*val);
>         int ret = 0;
>  
> -       if (nregbuf > maxregbuf)
> +       if (nregbuf > sizeof(regbuf))
>                 return -EINVAL;
>  
>         regbuf[0] = reg >> 8;
> 
> Let me know if you're happy with that; I can merge it to the original
> patch.

Yes, thanks.

> 
>>>>> +	u8 nregbuf = sizeof(reg) + num * sizeof(*val);
>>>>> +	int ret = 0;
>>>>> +
>>>>> +	if (nregbuf > maxregbuf)
>>>>> +		return -EINVAL;
>>>>> +
>>>>> +	regbuf[0] = reg >> 8;
>>>>> +	regbuf[1] = reg & 0xff;
>>>>> +
>>>>> +	memcpy(regbuf + 2, val, num);
>>>>> +
>>>>> +	ret = i2c_master_send(ov7251->i2c_client, regbuf, nregbuf);
>>>>> +	if (ret < 0) {
>>>>> +		dev_err(ov7251->dev, "%s: write seq regs error %d: first reg=%x\n",
>>>>
>>>> This line is over 80... 
>>>
>>> Yes indeed. Somehow checkpatch does not report this line, I don't know why.
>>>
>>>>
>>>> If you're happy with these, I can make the changes, too; they're trivial.
>>>
>>> Only the second one? Thanks :)
>>
>> Works for me. I'd still think the overhead of managing the buffer is
>> irrelevant where to having an extra function to do essentially the same
>> thing is a source of maintenance and review work. Note that we're even now
>> spending time to discuss it. ;-)
>>
>> -- 
>> Kind regards,
>>
>> Sakari Ailus
>> e-mail: sakari.ailus@....fi
> 

-- 
Best regards,
Todor Tomov