linux-kernel - Re: [PATCH] drm/fb_cma_helper: Implement fb

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Date:	Tue, 7 Jun 2016 16:43:05 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Robin Murphy <robin.murphy@....com>
Cc:	airlied@...ux.ie, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, daniel.vetter@...ll.ch,
	liviu.dudau@....com
Subject: Re: [PATCH] drm/fb_cma_helper: Implement fb_mmap callback

On Tue, Jun 07, 2016 at 01:18:09PM +0100, Robin Murphy wrote:
> In the absence of an fb_mmap callback, the fbdev code falls back to a
> naive implementation which relies upon the DMA address being the same
> as the physical address, and the buffer being physically contiguous
> from there. Whilst this often holds for standard CMA allocations via
> the platform's regular DMA ops, if the allocation is provided by an
> IOMMU then such assumptions can fall apart spectacularly.
> 
> To resolve this, reroute the fb_mmap call to the appropriate DMA API
> implementation, as per the other cma_helper calls.
> 
> Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> 
> Resending rebased to 4.7-rc1 with Daniel's ack. I know Russell raised
> some concerns about the general way fb_cma_helper uses fb_info[1], but
> AFAICS that's a longstanding separate problem orthogonal to this patch.

Do you want me to pull this in through drm-misc, or will this land through
some driver tree? Note that I'll do -misc pulls about every week, so if
you don't send your pull this week I'd like to pull it in to avoid
hilarity^W needless conflicts.
-Daniel

> 
> Robin.
> 
> [1]:http://thread.gmane.org/gmane.comp.video.dri.devel/149288
> 
>  drivers/gpu/drm/drm_fb_cma_helper.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fb_cma_helper.c b/drivers/gpu/drm/drm_fb_cma_helper.c
> index 172cafe11c71..a25afc068d3f 100644
> --- a/drivers/gpu/drm/drm_fb_cma_helper.c
> +++ b/drivers/gpu/drm/drm_fb_cma_helper.c
> @@ -23,6 +23,7 @@
>  #include <drm/drm_crtc_helper.h>
>  #include <drm/drm_gem_cma_helper.h>
>  #include <drm/drm_fb_cma_helper.h>
> +#include <linux/dma-mapping.h>
>  #include <linux/module.h>
>  
>  #define DEFAULT_FBDEFIO_DELAY_MS 50
> @@ -297,6 +298,12 @@ int drm_fb_cma_debugfs_show(struct seq_file *m, void *arg)
>  EXPORT_SYMBOL_GPL(drm_fb_cma_debugfs_show);
>  #endif
>  
> +static int drm_fb_cma_mmap(struct fb_info *info, struct vm_area_struct *vma)
> +{
> +	return dma_mmap_writecombine(info->device, vma, info->screen_base,
> +				     info->fix.smem_start, info->fix.smem_len);
> +}
> +
>  static struct fb_ops drm_fbdev_cma_ops = {
>  	.owner		= THIS_MODULE,
>  	.fb_fillrect	= drm_fb_helper_sys_fillrect,
> @@ -307,6 +314,7 @@ static struct fb_ops drm_fbdev_cma_ops = {
>  	.fb_blank	= drm_fb_helper_blank,
>  	.fb_pan_display	= drm_fb_helper_pan_display,
>  	.fb_setcmap	= drm_fb_helper_setcmap,
> +	.fb_mmap	= drm_fb_cma_mmap,
>  };
>  
>  static int drm_fbdev_cma_deferred_io_mmap(struct fb_info *info,
> -- 
> 2.8.1.dirty
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch