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

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Date:	Tue, 7 Jun 2016 16:03:40 +0100
From:	Robin Murphy <robin.murphy@....com>
To:	airlied@...ux.ie, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, liviu.dudau@....com
Subject: Re: [PATCH] drm/fb_cma_helper: Implement fb_mmap callback

On 07/06/16 15:43, Daniel Vetter wrote:
> 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.

Yeah, drm-misc sounds appropriate so if you're happy to pick it up, 
please feel free :)

Robin.

> -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
>>
>