[PATCH] drm: tilcdc: Calculate the vrefresh if it is not set by userspace

[Jyri Sarha]


Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

On 10/10/17 15:09, Kevin Hao wrote:
> The check for vrefresh has been removed by commit 11abbc9f39e0
> ("drm/tilcdc: Set framebuffer DMA address to HW only if CRTC is
> enabled"). But the userspace is really possible to request a display
> mode with vrefresh uninitialized, then it would cause the following
> calltrace:
>   [<c010fa20>] (unwind_backtrace) from [<c010c508>] (show_stack+0x20/0x24)
>   [<c010c508>] (show_stack) from [<c0959744>] (dump_stack+0x20/0x28)
>   [<c0959744>] (dump_stack) from [<c010c23c>] (__div0+0x20/0x28)
>   [<c010c23c>] (__div0) from [<c095805c>] (Ldiv0+0x8/0x14)
>   [<c095805c>] (Ldiv0) from [<c0615ccc>] (tilcdc_crtc_update_fb+0xa8/0x1d4)
>   [<c0615ccc>] (tilcdc_crtc_update_fb) from [<c0614b70>] (tilcdc_plane_atomic_update+0x54/0x5c)
>   [<c0614b70>] (tilcdc_plane_atomic_update) from [<c05c53a4>] (drm_atomic_helper_commit_planes+0x1b4/0x270)
>   [<c05c53a4>] (drm_atomic_helper_commit_planes) from [<c0617d48>] (tilcdc_commit+0x58/0x84)
>   [<c0617d48>] (tilcdc_commit) from [<c05e3f08>] (drm_atomic_commit+0x54/0x68)
>   [<c05e3f08>] (drm_atomic_commit) from [<c05c937c>] (drm_atomic_helper_set_config+0x68/0x9c)
>   [<c05c937c>] (drm_atomic_helper_set_config) from [<c05d843c>] (__drm_mode_set_config_internal+0x60/0xe0)
>   [<c05d843c>] (__drm_mode_set_config_internal) from [<c05d906c>] (drm_mode_setcrtc+0x3a8/0x4c0)
>   [<c05d906c>] (drm_mode_setcrtc) from [<c05d3c2c>] (drm_ioctl_kernel+0x78/0xb0)
>   [<c05d3c2c>] (drm_ioctl_kernel) from [<c05d3e60>] (drm_ioctl+0x1fc/0x328)
>   [<c05d3e60>] (drm_ioctl) from [<c0280008>] (vfs_ioctl+0x28/0x44)
>   [<c0280008>] (vfs_ioctl) from [<c0280a00>] (do_vfs_ioctl+0x890/0x8ec)
>   [<c0280a00>] (do_vfs_ioctl) from [<c0280abc>] (SyS_ioctl+0x60/0x7c)
>   [<c0280abc>] (SyS_ioctl) from [<c01078e0>] (ret_fast_syscall+0x0/0x48)
> 
> So calculate the vrefresh in mode_fixup() to make sure there always
> have a valid vrefresh.
> 

The earlier check was there for the frame buffer updates when the
display is not yet enabled and the hwmode's vrefresh is not valid yet.
Now, with the lock protected enabled state variable check, this should
never happen.

Do you have a reliable way to reproduce the problem you are seeing?
Could try adding a test for the vrefresh validity in the
tilcdc_crtc_mode_valid() to see if that helps?

Adding the extra test in the mode validity check probably produces a
failed mode set attempt, which I guess is Ok if the mode has zero
vertical refresh time. But if this does not help, then the issue you are
seeing may be an indication of a synchronization problem somewhere.

Best regards,
Jyri

> Fixes: 11abbc9f39e0 ("drm/tilcdc: Set framebuffer DMA address to HW only if CRTC is enabled")
> Cc: <stable at vger.kernel.org> # v4.11+
> Signed-off-by: Kevin Hao <kexin.hao at windriver.com>
> ---
>  drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> index d2589f310437..16b020a9044c 100644
> --- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> +++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c
> @@ -690,6 +690,9 @@ static bool tilcdc_crtc_mode_fixup(struct drm_crtc *crtc,
>  		adjusted_mode->flags &= ~DRM_MODE_FLAG_PHSYNC;
>  	}
>  
> +	if (!adjusted_mode->vrefresh)
> +		adjusted_mode->vrefresh = drm_mode_vrefresh(adjusted_mode);
> +
>  	return true;
>  }
>  
>