Re: [PATCH] drm/i915: fix overlay on i830M

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Oct 22, 2012 at 12:55:55PM +0200, Daniel Vetter wrote:
> The overlay on the i830M has a peculiar failure mode: It works the
> first time around after boot-up, but consistenly hangs the second time
> it's used.
> 
> Chris Wilson has dug out a nice errata:
> 
> "1.5.12 Clock Gating Disable for Display Register
> Address Offset:	06200h–06203h
> 
> "Bit 3
> Ovrunit Clock Gating Disable.
> 0 = Clock gating controlled by unit enabling logic
> 1 = Disable clock gating function
> DevALM Errata ALM049: Overlay Clock Gating Must be Disabled:  Overlay
> & L2 Cache clock gating must be disabled in order to prevent device
> hangs when turning off overlay.SW must turn off Ovrunit clock gating
> (6200h) and L2 Cache clock gating (C8h)."
> 
> Now I've nowhere found that 0xc8 register and hence couldn't apply the
> l2 cache workaround. But I've remembered that part of the magic that
> the OVERLAY_ON/OFF commands are supposed to do is to rearrange cache
> allocations so that the overlay scaler has some scratch space.
> 
> And while pondering how that could explain the hang the 2nd time we
> enable the overlay, I've remembered that the old ums overlay code did
> _not_ issue the OVERLAY_OFF cmd.
> 
> And indeed, disabling the OFF cmd results in the overlay working
> flawlessly, so I guess we can workaround the lack of the above
> workaround by simply never disabling the overlay engine once it's
> enabled.
> 
> v2: Add a comment in the code.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=47827
> Cc: stable@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Tested-by: Rhys <rhyspuk@gmail.com>

> ---
>  drivers/gpu/drm/i915/intel_overlay.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_overlay.c b/drivers/gpu/drm/i915/intel_overlay.c
> index 555912f..e3b095f 100644
> --- a/drivers/gpu/drm/i915/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/intel_overlay.c
> @@ -342,9 +342,17 @@ static int intel_overlay_off(struct intel_overlay *overlay)
>  	intel_ring_emit(ring, flip_addr);
>  	intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
>  	/* turn overlay off */
> -	intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_OFF);
> -	intel_ring_emit(ring, flip_addr);
> -	intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
> +	if (IS_I830(dev)) {
> +		/* Workaround: Don't disable the overlay fully, since otherwise
> +		 * it dies on the next OVERLAY_ON cmd. */
> +		intel_ring_emit(ring, MI_NOOP);
> +		intel_ring_emit(ring, MI_NOOP);
> +		intel_ring_emit(ring, MI_NOOP);
> +	} else {
> +		intel_ring_emit(ring, MI_OVERLAY_FLIP | MI_OVERLAY_OFF);
> +		intel_ring_emit(ring, flip_addr);
> +		intel_ring_emit(ring, MI_WAIT_FOR_EVENT | MI_WAIT_FOR_OVERLAY_FLIP);
> +	}
>  	intel_ring_advance(ring);
>  
>  	return intel_overlay_do_wait_request(overlay, intel_overlay_off_tail);
> -- 
> 1.7.11.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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