linux-kernel - Re: [PATCH] video/smscufx: fix line counting in fb

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Date:	Thu, 26 Jul 2012 17:26:49 +0000
From:	Florian Tobias Schandinat <FlorianSchandinat@....de>
To:	Alexander Holler <holler@...oftware.de>
CC:	linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH] video/smscufx: fix line counting in fb_write

On 07/02/2012 09:25 PM, Alexander Holler wrote:
> Hi Florian,
> 
> sorry for the late answer.
> 
> Am 13.05.2012 14:47, schrieb Florian Tobias Schandinat:
>> Hi Alexander,
>>
>> On 04/21/2012 11:26 AM, Alexander Holler wrote:
>>> Hello,
>>>
>>> as for the patch for udlfb, I forgot to mention that this is a candidate
>>> for all stable trees 3.2 and above.
>>>
>>> Btw., the address of the maintainer doesn't seem to be valid anymore.
>>
>> it is better to cc me on patches to the framebuffer subsystem for such
>> cases. I don't have much free time so it's rare that I come around to
>> dig in the mailing list.
>>
>>>
>>> Regards,
>>>
>>> Alexander
>>>
>>> Am 21.04.2012 00:11, schrieb Alexander Holler:
>>>> Line 0 and 1 were both written to line 0 (on the display) and all
>>>> subsequent
>>>> lines had an offset of -1. The result was that the last line on the
>>>> display
>>>> was never overwritten by writes to /dev/fbN.
>>>>
>>>> The origin of this bug seems to have been udlfb.
>>>>
>>>> Signed-off-by: Alexander Holler<holler@...oftware.de>
>>>
>>> Cc: stable@...r.kernel.org
>>
>> Patch looks good to me but can be made simpler.
>>
>>>
>>>> ---
>>>>    drivers/video/smscufx.c |    2 +-
>>>>    1 files changed, 1 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/drivers/video/smscufx.c b/drivers/video/smscufx.c
>>>> index ccbfef5..1e1e2d2 100644
>>>> --- a/drivers/video/smscufx.c
>>>> +++ b/drivers/video/smscufx.c
>>>> @@ -904,7 +904,7 @@ static ssize_t ufx_ops_write(struct fb_info *info,
>>>> const char __user *buf,
>>>>        result = fb_sys_write(info, buf, count, ppos);
>>>>
>>>>        if (result>  0) {
>>>> -        int start = max((int)(offset / info->fix.line_length) - 1, 0);
>>>> +        int start = max((int)(offset / info->fix.line_length), 0);
>>
>> the cast to int as well as the max is superfluous without the -1 as the
>> value can no longer be negative.
> 
> I had that impression too, but I wanted to change as less as possible,
> so I didn't had the need to check types and (their) sizes for possible
> overflows or such. I was lazy and just wanted to fix that one bug. ;)

Well, as this patch fixes a bug I applied it as is.

> 
>>
>>>>            int lines = min((u32)((result / info->fix.line_length) + 1),
>>>>                    (u32)info->var.yres);
>>>>


Best regards,

Florian Tobias Schandinat
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