Re: [PATCH v2] RFC: framebuffer: provide generic get_fb_unmapped_area
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From: David Herrmann <hidden>
Date: 2014-03-17 12:15:04
Hi On Mon, Feb 3, 2014 at 6:14 PM, Uwe Kleine-König [off-list ref] wrote:
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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 <redacted> --- 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
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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 -- To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html