linux-kernel - Re: [PATCH v4 03/13] media: pci: cx18-av-vbi: Replace open-coded parity calculation with parity

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Message-ID: <7d0096ad-a290-4fbc-8c06-dba49e8db8af@xs4all.nl>
Date: Fri, 25 Apr 2025 10:51:05 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Kuan-Wei Chiu <visitorckw@...il.com>,
 Arend van Spriel <arend.vanspriel@...adcom.com>
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 andrew.cooper3@...rix.com, Yu-Chun Lin <eleanor15x@...il.com>
Subject: Re: [PATCH v4 03/13] media: pci: cx18-av-vbi: Replace open-coded
 parity calculation with parity_odd()

On 09/04/2025 20:59, Kuan-Wei Chiu wrote:
> On Wed, Apr 09, 2025 at 08:43:09PM +0200, Arend van Spriel wrote:
>> On 4/9/2025 5:43 PM, Kuan-Wei Chiu wrote:
>>> Refactor parity calculations to use the standard parity_odd() helper.
>>> This change eliminates redundant implementations.
>>>
>>> Co-developed-by: Yu-Chun Lin <eleanor15x@...il.com>
>>> Signed-off-by: Yu-Chun Lin <eleanor15x@...il.com>
>>> Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
>>> ---
>>>   drivers/media/pci/cx18/cx18-av-vbi.c | 12 ++----------
>>>   1 file changed, 2 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/media/pci/cx18/cx18-av-vbi.c b/drivers/media/pci/cx18/cx18-av-vbi.c
>>> index 65281d40c681..15b515b95956 100644
>>> --- a/drivers/media/pci/cx18/cx18-av-vbi.c
>>> +++ b/drivers/media/pci/cx18/cx18-av-vbi.c
>>
>> [...]
>>
>>> @@ -278,7 +270,7 @@ int cx18_av_decode_vbi_line(struct v4l2_subdev *sd,
>>>   		break;
>>>   	case 6:
>>>   		sdid = V4L2_SLICED_CAPTION_525;
>>> -		err = !odd_parity(p[0]) || !odd_parity(p[1]);
>>> +		err = !parity_odd(p[0]) || !parity_odd(p[1]);
>>
>> No need to call parity_odd() twice here. Instead you could do:
>>
>> 		err = !parity_odd(p[0] ^ p[1]);

I prefer the original approach, it is easier to understand. Performance
is not an issue here, clarity of the code is more important.

So for this patch (i.e. this v4 version):

Reviewed-by: Hans Verkuil <hverkuil@...all.nl>

>>
>> This is orthogonal to the change to parity_odd() though. More specific to
>> the new parity_odd() you can now do following as parity_odd() argument is
>> u64:
>>
>> 		err = !parity_odd(*(u16 *)p);
>>
>>
> Thanks for the feedback!
> Would you prefer this change to be part of the parity() conversion
> patch, or in a separate one?

Just leave it as-is, as mentioned above.

Regards,

	Hans

> 
> Regards,
> Kuan-Wei