[PATCH] drm/fb-helper: Mark screen buffers in system memory with FB_VIRTFB

[Daniel Vetter]

On Thu, Jan 27, 2022 at 11:26:21AM +0100, Thomas Zimmermann wrote:
> Mark screen buffers in system memory with FB_VIRTFB. Otherwise, the
> buffers are mmap'ed as I/O memory (i.e., VM_IO). For shadow buffers,
> also set the FB_READS_FAST hint.

Maybe clarify that this only holds for the defio case, and since we have
our own shadow copy for that anyway it shouldn't matter. I'm also not sure
how much the memcpy gains us compared to just redrawing ...

What's the motivation here, or just something you spotted?
-Daniel

> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index ed43b987d306..f15127a32f7a 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -2346,6 +2346,7 @@ static int drm_fb_helper_generic_probe(struct drm_fb_helper *fb_helper,
>  	fbi->fbops = &drm_fbdev_fb_ops;
>  	fbi->screen_size = sizes->surface_height * fb->pitches[0];
>  	fbi->fix.smem_len = fbi->screen_size;
> +	fbi->flags = FBINFO_DEFAULT;
>  
>  	drm_fb_helper_fill_info(fbi, fb_helper, sizes);
>  
> @@ -2353,19 +2354,21 @@ static int drm_fb_helper_generic_probe(struct drm_fb_helper *fb_helper,
>  		fbi->screen_buffer = vzalloc(fbi->screen_size);
>  		if (!fbi->screen_buffer)
>  			return -ENOMEM;
> +		fbi->flags |= FBINFO_VIRTFB | FBINFO_READS_FAST;
>  
>  		fbi->fbdefio = &drm_fbdev_defio;
> -
>  		fb_deferred_io_init(fbi);
>  	} else {
>  		/* buffer is mapped for HW framebuffer */
>  		ret = drm_client_buffer_vmap(fb_helper->buffer, &map);
>  		if (ret)
>  			return ret;
> -		if (map.is_iomem)
> +		if (map.is_iomem) {
>  			fbi->screen_base = map.vaddr_iomem;
> -		else
> +		} else {
>  			fbi->screen_buffer = map.vaddr;
> +			fbi->flags |= FBINFO_VIRTFB;
> +		}
>  
>  		/*
>  		 * Shamelessly leak the physical address to user-space. As
> -- 
> 2.34.1
> 

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