linux-kernel - Re: [PATCH] drm/bochs: fix bochs_gem_prime

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Date:   Tue, 5 Feb 2019 10:01:28 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR BOCHS VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/bochs: fix bochs_gem_prime_mmap

On Mon, Feb 04, 2019 at 07:38:58PM +0100, Gerd Hoffmann wrote:
> ttm_fbdev_mmap() just doesn't work.  It appears to work fine, mmap()
> returns success, but any attempt to actually access the mapping causes a
> SIGBUS.
> 
> We can just use drm_gem_prime_mmap() instead.  Almost.  We have to copy
> over the start offset from the ttm_buffer_object vm_node to the
> drm_gem_object vm_node so the offset math in drm_gem_prime_mmap() works
> correctly for us even though we use ttm to manage our objects.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>

Would be kinda neat if we could teach ttm to not have it's own vma node
...

Anyway, lgtm.

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>

> ---
>  drivers/gpu/drm/bochs/bochs_mm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bochs/bochs_mm.c b/drivers/gpu/drm/bochs/bochs_mm.c
> index 641a33f134..49463348a0 100644
> --- a/drivers/gpu/drm/bochs/bochs_mm.c
> +++ b/drivers/gpu/drm/bochs/bochs_mm.c
> @@ -442,5 +442,6 @@ int bochs_gem_prime_mmap(struct drm_gem_object *obj,
>  {
>  	struct bochs_bo *bo = gem_to_bochs_bo(obj);
>  
> -	return ttm_fbdev_mmap(vma, &bo->bo);
> +	bo->gem.vma_node.vm_node.start = bo->bo.vma_node.vm_node.start;
> +	return drm_gem_prime_mmap(obj, vma);
>  }
> -- 
> 2.9.3
> 

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