[PATCH v2] RFC: framebuffer: provide generic get_fb_unmapped_area

[PATCH v2] RFC: framebuffer: provide generic get_fb_unmapped_area

[Uwe Kleine-König]

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@pengutronix.de>
---
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
+
 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

Re: [PATCH v2] RFC: framebuffer: provide generic get_fb_unmapped_area

[Uwe Kleine-König]

On Mon, Feb 03, 2014 at 06:14:44PM +0100, Uwe Kleine-König 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@pengutronix.de>
> ---
> 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.
Do you still have this patch on your radar?

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
> +
>  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
> 
> 

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: [PATCH v2] RFC: framebuffer: provide generic get_fb_unmapped_area

[Tomi Valkeinen]

[-- Attachment #1: Type: text/plain, Size: 1031 bytes --]

Hi,

On 03/02/14 19:14, Uwe Kleine-König 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@pengutronix.de>
> ---
> 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.

I don't know enough about mm to say much here, and the text above make
me feel a bit uneasy. I'd be happy if this would get a few
acks/reviewed-bys/tested-bys...

So what does this patch actually do? If I read things correctly,
currently .get_unmapped_area is null, except for sparc and blackfin. But
userspace's mmap() calls that, right? Is there a default implementation
somewhere? Why is that different for no-MMU case?

 Tomi



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Re: [PATCH v2] RFC: framebuffer: provide generic get_fb_unmapped_area

[David Herrmann]

Hi

On Mon, Feb 3, 2014 at 6:14 PM, Uwe Kleine-König
<u.kleine-koenig@pengutronix.de> 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@pengutronix.de>
> ---
> 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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