Re: [PATCH 3/3] drm/tegra: fb: Implement ->fb_mmap() callback

[Marcel Ziswiler <marcel.ziswiler-2KBjVHiyJgBBDgjK7y7TUQ@public.gmane.org>]

On Wed, 2018-02-07 at 18:45 +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> This fixes hangs with legacy applications that use the mmap() syscall
> on
> the fbdev device to map framebuffer memory. The fbdev implementation
> for
> mmap() creates a mapping that conflicts with DRM usage and causes a
> hang
> when the memory is accessed through the mapping.

With that legacy Qt4e applications run just fine now on Apalis TK1
running Linux kernel 4.14.18.

Thanks, Thierry!

Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>

Reported-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>  drivers/gpu/drm/tegra/fb.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tegra/fb.c b/drivers/gpu/drm/tegra/fb.c
> index 001cb77e2f59..0786159edef3 100644
> --- a/drivers/gpu/drm/tegra/fb.c
> +++ b/drivers/gpu/drm/tegra/fb.c
> @@ -224,12 +224,28 @@ struct drm_framebuffer *tegra_fb_create(struct
> drm_device *drm,
>  }
>  
>  #ifdef CONFIG_DRM_FBDEV_EMULATION
> +static int tegra_fb_mmap(struct fb_info *info, struct vm_area_struct
> *vma)
> +{
> +	struct drm_fb_helper *helper = info->par;
> +	struct tegra_bo *bo;
> +	int err;
> +
> +	bo = tegra_fb_get_plane(helper->fb, 0);
> +
> +	err = drm_gem_mmap_obj(&bo->gem, bo->gem.size, vma);
> +	if (err < 0)
> +		return err;
> +
> +	return __tegra_gem_mmap(&bo->gem, vma);
> +}
> +
>  static struct fb_ops tegra_fb_ops = {
>  	.owner = THIS_MODULE,
>  	DRM_FB_HELPER_DEFAULT_OPS,
>  	.fb_fillrect = drm_fb_helper_sys_fillrect,
>  	.fb_copyarea = drm_fb_helper_sys_copyarea,
>  	.fb_imageblit = drm_fb_helper_sys_imageblit,
> +	.fb_mmap = tegra_fb_mmap,
>  };
>  
>  static int tegra_fbdev_probe(struct drm_fb_helper *helper,