Re: [PATCH 20/24] drm/i915: kill bogus GTIIR clearing in vlv_preinstall hook

[Ben Widawsky <ben@bwidawsk.net>]

On Wed, Jun 12, 2013 at 01:37:22PM +0200, Daniel Vetter wrote:
> Preinstall disables interrupts, we clear the status register in the
> postinstall hook before we actually enable interrupt sources.
> 
> Also add a comment for the curios ring IMR masking, it doesn't
> seem to be required on any other platform.
> 
> We seem to have some room for common gt_preinstall/postinstall hooks.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 293ee68..b680e1c 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2546,13 +2546,12 @@ static void valleyview_irq_preinstall(struct drm_device *dev)
>  
>  	/* VLV magic */
>  	I915_WRITE(VLV_IMR, 0);
> +	/* Do we really need to clear ring masks for vlv? */
>  	I915_WRITE(RING_IMR(RENDER_RING_BASE), 0);
>  	I915_WRITE(RING_IMR(GEN6_BSD_RING_BASE), 0);
>  	I915_WRITE(RING_IMR(BLT_RING_BASE), 0);

I actually like this for all GENs with rings as a documentation kind of
thing.

>  
>  	/* and GT */
> -	I915_WRITE(GTIIR, I915_READ(GTIIR));
> -	I915_WRITE(GTIIR, I915_READ(GTIIR));
>  	I915_WRITE(GTIMR, 0xffffffff);
>  	I915_WRITE(GTIER, 0x0);
>  	POSTING_READ(GTIER);

The ordering was wrong here anyway. I think to have the desired effect
it should have been
1. mask
2. disable
3. posting read
4. clear
5. posting read
6. clear // potential pending irq

But one thing this changes is the double clear, which I feel might be
necessary if it is meant to clear the pending interrupt as I would
guess. We only seem to do one in postinstall. If this change was
intentional, I think we should get Jesse to explain the origin of the
original double clear.

-- 
Ben Widawsky, Intel Open Source Technology Center