Re: [PATCH] drm: rcar-du: Fix R-Car Gen3 crash when VSP is disabled

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Magnus,

On Tuesday 06 Dec 2016 16:07:02 Laurent Pinchart wrote:
> On Wednesday 26 Oct 2016 18:13:23 Magnus Damm wrote:
> > On Wed, Oct 26, 2016 at 4:31 PM, Geert Uytterhoeven wrote:
> >> On Wed, Oct 26, 2016 at 5:31 AM, Magnus Damm wrote:
> >>> From: Magnus Damm <damm+renesas@opensource.se>
> >>> 
> >>> For the DU to operate on R-Car Gen3 hardware a combination of DU
> >>> and VSP devices are required. Since the DU driver also supports
> >>> earlier generations hardware the VSP portion is enabled via Kconfig.
> >>> 
> >>> The arm64 defconfig is as of v4.9-rc1 having the DU driver enabled
> >>> as a module, however this is not enough to support R-Car Gen3. In
> >>> the current case of CONFIG_DRM_RCAR_VSP=n then the kernel crashes
> >>> when loading the module. This patch is fixing that particular case.
> >>> 
> >>> In more detail, the crash triggers in drm_atomic_get_plane_state()
> >>> when __drm_atomic_helper_set_config() passes NULL as crtc->primary.
> >>> 
> >>> This patch corrects this issue by failing to load the DU driver on
> >>> R-Car Gen3 when VSP is not available.
> >>> 
> >>> Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
> >>> ---
> >>> 
> >>>  drivers/gpu/drm/rcar-du/rcar_du_vsp.h |    2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>> 
> >>> --- 0001/drivers/gpu/drm/rcar-du/rcar_du_vsp.h
> >>> +++ work/drivers/gpu/drm/rcar-du/rcar_du_vsp.h  2016-10-26
> >>> 00:01:12.920607110 +0900 @@ -70,7 +70,7 @@ void
> >>> rcar_du_vsp_disable(struct rcar_du_
> >>> 
> >>>  void rcar_du_vsp_atomic_begin(struct rcar_du_crtc *crtc);
> >>>  void rcar_du_vsp_atomic_flush(struct rcar_du_crtc *crtc);
> >>>  #else
> >>> 
> >>> -static inline int rcar_du_vsp_init(struct rcar_du_vsp *vsp) { return
> >>> 0;
> >>> };
> >>> +static inline int rcar_du_vsp_init(struct rcar_du_vsp *vsp) { return
> >>> -ENXIO; };
> 
> With this patch applied the DU will fail to probe on Gen2 if DRM_RCAR_VSP is
> disabled.
> 
> DRM_RCAR_DU should instead depend on VIDEO_RENESAS_VSP1 (with DRM_RCAR_VSP
> always set) on Gen3.

Do you plan to work on a v2 that fixes this in Kconfig ? I gave it a quick try 
but ran into a Kconfig circular dependency that I don't have time to debug 
now.

> > > -ENODEV sounds more appropriate
> > 
> > Ok, however -ENXIO is the same error code as the DU driver currently
> > returns when dealing with the VSP and not finding DT nodes.
> > 
> > To avoid dealing with this again I would prefer skipping per-driver
> > Kconfig options entirely, for instance something like this:
> > 
> > [PATCH/RFC] Simplify Gen3 DU and VSP Kconfig bits
> > https://www.spinics.net/lists/linux-sh/msg45978.html
> > 
> >>>  static inline void rcar_du_vsp_enable(struct rcar_du_crtc *crtc) { };
> >>>  static inline void rcar_du_vsp_disable(struct rcar_du_crtc *crtc) { };
> >>>  static inline void rcar_du_vsp_atomic_begin(struct rcar_du_crtc *crtc)
> >>>  {
> >>>  };
> >> 
> >> Alternatively,  DRM_RCAR_DU can force DRM_RCAR_VSP to y if ARCH_R8A7795
> >> or ARCH_R8A7796 is enabled.
> > 
> > The DU driver has symbol dependencies on VSP and FCP driver code
> > (V4L2), so we need to take the state of driver support for those
> > modules into consideration as well instead of only depending on
> > SoC-specific Kconfig symbols.
> > 
> > On Wed, Oct 26, 2016 at 4:31 PM, Geert Uytterhoeven wrote:
> >> On Wed, Oct 26, 2016 at 5:31 AM, Magnus Damm wrote:
> >>> The arm64 defconfig is as of v4.9-rc1 having the DU driver enabled
> >>> as a module, however this is not enough to support R-Car Gen3. In
> >> 
> >> Nope, arm64 defconfig on v4.9-rc1:
> >> # CONFIG_DRM_RCAR_DU is not set
> > 
> > Right, you are correct. Sorry for the noise. It seems that I was using
> > renesas-drivers-2016-10-18-v4.9-rc1 - not mainline v4.9-rc1.
> > 
> > Without this fix the driver still crashes, but not due to defconfig in
> > v4.9-rc1.

-- 
Regards,

Laurent Pinchart