Hi
On Mon, Feb 3, 2014 at 6:14 PM, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> This patch makes mmapping the simple-framebuffer device work on a no-MMU
> ARM target. The code is mostly taken from
> arch/blackfin/kernel/sys_bfin.c.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> ---
> Hello,
>
> note this is only tested on this no-MMU machine and I don't know enough
> about framebuffers and mm to decide if this patch is sane. Also I'm
> a bit unsure about the size check, I just believed Geert that
> PAGE_ALIGN(info->fix.smem_len) is the right value to check against.
>
> Best regards
> Uwe
>
> drivers/video/fbmem.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> index 7309ac704e26..d0ccedafec8c 100644
> --- a/drivers/video/fbmem.c
> +++ b/drivers/video/fbmem.c
> @@ -1491,6 +1491,22 @@ __releases(&info->lock)
> return 0;
> }
>
> +#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
> +#define fb_get_unmapped_area get_fb_unmapped_area
> +#else
> +unsigned long fb_get_unmapped_area(struct file *filp, unsigned long orig_addr,
> + unsigned long len, unsigned long pgoff, unsigned long flags)
> +{
> + struct fb_info * const info = filp->private_data;
> + unsigned long fb_size = PAGE_ALIGN(info->fix.smem_len);
> +
> + if (pgoff > fb_size || len > fb_size - pgoff)
> + return -EINVAL;
> +
> + return (unsigned long)info->screen_base + pgoff;
> +}
> +#endif
> +
Doesn't this break mmu systems? x86 for instance has no
get_fb_unmapped_area(), therefore f_ops->get_unmapped_area() is NULL
and thus falls back to the generic handler of the task (see
mm/mmap.c). If you replace this with your handler, _every_ mmap() call
with be treated as MAP_FIXED with "info->screen_base + pgoff" as
address. This might work in test-cases on the first mmap() call, but
any further call will fail.
Thanks
David
> static const struct file_operations fb_fops = {
> .owner = THIS_MODULE,
> .read = fb_read,
> @@ -1502,9 +1518,7 @@ static const struct file_operations fb_fops = {
> .mmap = fb_mmap,
> .open = fb_open,
> .release = fb_release,
> -#ifdef HAVE_ARCH_FB_UNMAPPED_AREA
> - .get_unmapped_area = get_fb_unmapped_area,
> -#endif
> + .get_unmapped_area = fb_get_unmapped_area,
> #ifdef CONFIG_FB_DEFERRED_IO
> .fsync = fb_deferred_io_fsync,
> #endif
> --
> 1.8.5.2
>
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