Re: [PATCH 3/3] [media] tw68: don't assume that pagesize is always 4096

[Hans Verkuil <hverkuil@xs4all.nl>]

On 09/04/2014 04:46 PM, Mauro Carvalho Chehab wrote:
> This code implicitly assumes that pagesize is 4096, but this is
> not true on all archs, as the PAGE_SHIFT can be different than
> 12 on all those architectures: alpha, arc, arm64, cris, frv,
> hexagon,ia64, m68k, metag, microblaze, mips, openrisc, parisc,
> powerpc, sh, sparc and tile.
> 
> The real constrant here seems to be to limit the buffer size to
> 4MB.
> 
> So, fix the code to reflect that, in a way that it will keep
> working with differnt values for PAGE_SIZE.

While your fix is OK, I have a better patch that makes the code a lot more
readable. I'll post that soon.

Regards,

	Hans

> 
> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
> 
> diff --git a/drivers/media/pci/tw68/tw68-video.c b/drivers/media/pci/tw68/tw68-video.c
> index 4dd38578cf1b..66658accdca9 100644
> --- a/drivers/media/pci/tw68/tw68-video.c
> +++ b/drivers/media/pci/tw68/tw68-video.c
> @@ -366,7 +366,7 @@ static int tw68_buffer_pages(int size)
>  {
>  	size  = PAGE_ALIGN(size);
>  	size += PAGE_SIZE; /* for non-page-aligned buffers */
> -	size /= 4096;
> +	size /= PAGE_SIZE;
>  	return size;
>  }
>  
> @@ -376,7 +376,7 @@ static int tw68_buffer_count(unsigned int size, unsigned int count)
>  {
>  	unsigned int maxcount;
>  
> -	maxcount = 1024 / tw68_buffer_pages(size);
> +	maxcount = (4096 * 1024 / PAGE_SIZE) / tw68_buffer_pages(size);
>  	if (count > maxcount)
>  		count = maxcount;
>  	return count;
>