linux-kernel - Re: [PATCH 5/8] fbdev: fb_defio: Export fb_deferred_io

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Message-ID: <5717CB6D.8000708@tronnes.org>
Date:	Wed, 20 Apr 2016 20:33:17 +0200
From:	Noralf Trønnes <noralf@...nnes.org>
To:	dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
	laurent.pinchart@...asonboard.com, tomi.valkeinen@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/8] fbdev: fb_defio: Export fb_deferred_io_mmap


Den 20.04.2016 19:44, skrev Daniel Vetter:
> On Wed, Apr 20, 2016 at 05:25:26PM +0200, Noralf Trønnes wrote:
>> Export fb_deferred_io_mmap so drivers can change vma->vm_page_prot.
>> When the framebuffer memory is allocated using dma_alloc_writecombine()
>> instead of vmalloc(), I get cache syncing problems.
>> This solves it:
>>
>> static int drm_fbdev_cma_deferred_io_mmap(struct fb_info *info,
>> 					  struct vm_area_struct *vma)
>> {
>> 	fb_deferred_io_mmap(info, vma);
>> 	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> Hm, do we need pgpropt_writecombine? There recently was some discussion
> (on the arc platform) that fbdev pgprots need to be fixed up in fbdev
> code. I have no idea, just repeating from memory ...

I need it or else I get partial lines that doesn't get updated on the 
display.
fbdev code that doesn't set (struct fb_ops *)->fb_mmap, gets this for free
in the default fb_mmap implementation (drivers/video/fbdev/core/fbmem.c).
It calls fb_pgprotect() at the end which is an architecture specific
function that on many platforms uses pgprot_writecombine(), but not on all.
And looking at some of the fb_mmap implementations, some of them sets
vm_page_prot to nocache for instance, so I think the safest bet is to do
this here and not in the fbdev core. And we can't call fb_pgprotect() from
fb_deferred_io_mmap() either because we don't have access to the file
pointer that powerpc needs.
I think the case you refer to was solved with using fb_pgprotect() for
the platform in question and it didn't involve deferred io.

> -Daniel
>
>> 	return 0;
>> }
>>
>> Signed-off-by: Noralf Trønnes <noralf@...nnes.org>
>> ---
>>   drivers/video/fbdev/core/fb_defio.c | 3 ++-
>>   include/linux/fb.h                  | 1 +
>>   2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
>> index 57721c7..74b5bca 100644
>> --- a/drivers/video/fbdev/core/fb_defio.c
>> +++ b/drivers/video/fbdev/core/fb_defio.c
>> @@ -164,7 +164,7 @@ static const struct address_space_operations fb_deferred_io_aops = {
>>   	.set_page_dirty = fb_deferred_io_set_page_dirty,
>>   };
>>   
>> -static int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
>> +int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
>>   {
>>   	vma->vm_ops = &fb_deferred_io_vm_ops;
>>   	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
>> @@ -173,6 +173,7 @@ static int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
>>   	vma->vm_private_data = info;
>>   	return 0;
>>   }
>> +EXPORT_SYMBOL(fb_deferred_io_mmap);
>>   
>>   /* workqueue callback */
>>   static void fb_deferred_io_work(struct work_struct *work)
>> diff --git a/include/linux/fb.h b/include/linux/fb.h
>> index dfe8835..a964d07 100644
>> --- a/include/linux/fb.h
>> +++ b/include/linux/fb.h
>> @@ -673,6 +673,7 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
>>   }
>>   
>>   /* drivers/video/fb_defio.c */
>> +int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma);
>>   extern void fb_deferred_io_init(struct fb_info *info);
>>   extern void fb_deferred_io_open(struct fb_info *info,
>>   				struct inode *inode,
>> -- 
>> 2.2.2
>>