Re: [PATCH 03/20] drm/i915: use GEN8_IRQ_INIT on GEN5

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Mar 18, 2014 at 10:11:38AM -0700, Ben Widawsky wrote:
> On Fri, Mar 07, 2014 at 08:10:19PM -0300, Paulo Zanoni wrote:
> > From: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > 
> > And rename is to GEN5_IRQ_INIT.
> > 
> > We have discussed doing equivalent changes on July 2013, and I even
> > sent a patch series for this: "[PATCH 00/15] Unify interrupt register
> > init/reset". Now that the BDW code was merged, I have one more
> > argument in favor of these changes.
> > 
> > Here's what really changes with the Gen 5 IRQ init code:
> >   - We now clear the IIR registers at preinstall (they are also
> >     cleared at postinstall, but we will change that later).
> >   - We have an additional POSTING_READ at the IMR register.
> > 
> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_irq.c | 49 +++++++++++++++++++----------------------
> >  1 file changed, 23 insertions(+), 26 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index 852844d..7be7da1 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -80,12 +80,30 @@ static const u32 hpd_status_i915[] = { /* i915 and valleyview are the same */
> >  	[HPD_PORT_D] = PORTD_HOTPLUG_INT_STATUS
> >  };
> >  
> > +/*
> > + * IIR can theoretically queue up two events. Be paranoid.
> > + * Also, make sure callers of these macros have something equivalent to a
> > + * POSTING_READ on the IIR register.
> > + * */
> 
> I don't understand what you mean in this comment. If you're always going
> to sending a posting read after the second IIR write, why not just put
> it in the macro?

Bspec says if there's a 2nd interrupt queued up IMR/IER don't affect that
bit and it will show up /sometimes/ after the first bit has been cleared
from IIR. My best guess for that was "on the next read", hence the
POSTING_READ to make sure it happens.

Or do you mean something else?

In any case a bit of Bspec citation for this would be appropriate.
-Daniel

> 
> The reason it wasn't in my original macro is because we've done the
> posting read on IER, and IMR - so we're not going to get new interrupts.
> When the second IIR write lands is irrelevant. The POSTING_READ in
> between is to prevent the [probably impossible] case of the writes
> getting collapsed into one write.
> 
> > +#define GEN8_IRQ_INIT_NDX(type, which) do { \
> > +	I915_WRITE(GEN8_##type##_IMR(which), 0xffffffff); \
> > +	POSTING_READ(GEN8_##type##_IMR(which)); \
> > +	I915_WRITE(GEN8_##type##_IER(which), 0); \
> > +	I915_WRITE(GEN8_##type##_IIR(which), 0xffffffff); \
> > +	POSTING_READ(GEN8_##type##_IIR(which)); \
> > +	I915_WRITE(GEN8_##type##_IIR(which), 0xffffffff); \
> > +} while (0)
> > +
> >  #define GEN5_IRQ_INIT(type) do { \
> >  	I915_WRITE(type##IMR, 0xffffffff); \
> > +	POSTING_READ(type##IMR); \
> >  	I915_WRITE(type##IER, 0); \
> > -	POSTING_READ(type##IER); \
> > +	I915_WRITE(type##IIR, 0xffffffff); \
> > +	POSTING_READ(type##IIR); \
> > +	I915_WRITE(type##IIR, 0xffffffff); \
> >  } while (0)
> >  
> > +
> >  /* For display hotplug interrupt */
> >  static void
> >  ironlake_enable_display_irq(drm_i915_private_t *dev_priv, u32 mask)
> > @@ -2789,6 +2807,7 @@ static void gen5_gt_irq_preinstall(struct drm_device *dev)
> >  	GEN5_IRQ_INIT(GT);
> >  	if (INTEL_INFO(dev)->gen >= 6)
> >  		GEN5_IRQ_INIT(GEN6_PM);
> > +	POSTING_READ(GTIIR);
> >  }
> >  
> >  /* drm_dma.h hooks
> > @@ -2843,25 +2862,6 @@ static void gen8_irq_preinstall(struct drm_device *dev)
> >  	I915_WRITE(GEN8_MASTER_IRQ, 0);
> >  	POSTING_READ(GEN8_MASTER_IRQ);
> >  
> > -	/* IIR can theoretically queue up two events. Be paranoid */
> > -#define GEN8_IRQ_INIT_NDX(type, which) do { \
> > -		I915_WRITE(GEN8_##type##_IMR(which), 0xffffffff); \
> > -		POSTING_READ(GEN8_##type##_IMR(which)); \
> > -		I915_WRITE(GEN8_##type##_IER(which), 0); \
> > -		I915_WRITE(GEN8_##type##_IIR(which), 0xffffffff); \
> > -		POSTING_READ(GEN8_##type##_IIR(which)); \
> > -		I915_WRITE(GEN8_##type##_IIR(which), 0xffffffff); \
> > -	} while (0)
> > -
> > -#define GEN8_IRQ_INIT(type) do { \
> > -		I915_WRITE(GEN8_##type##_IMR, 0xffffffff); \
> > -		POSTING_READ(GEN8_##type##_IMR); \
> > -		I915_WRITE(GEN8_##type##_IER, 0); \
> > -		I915_WRITE(GEN8_##type##_IIR, 0xffffffff); \
> > -		POSTING_READ(GEN8_##type##_IIR); \
> > -		I915_WRITE(GEN8_##type##_IIR, 0xffffffff); \
> > -	} while (0)
> > -
> >  	GEN8_IRQ_INIT_NDX(GT, 0);
> >  	GEN8_IRQ_INIT_NDX(GT, 1);
> >  	GEN8_IRQ_INIT_NDX(GT, 2);
> > @@ -2871,12 +2871,9 @@ static void gen8_irq_preinstall(struct drm_device *dev)
> >  		GEN8_IRQ_INIT_NDX(DE_PIPE, pipe);
> >  	}
> >  
> > -	GEN8_IRQ_INIT(DE_PORT);
> > -	GEN8_IRQ_INIT(DE_MISC);
> > -	GEN8_IRQ_INIT(PCU);
> > -#undef GEN8_IRQ_INIT
> > -#undef GEN8_IRQ_INIT_NDX
> > -
> > +	GEN5_IRQ_INIT(GEN8_DE_PORT_);
> > +	GEN5_IRQ_INIT(GEN8_DE_MISC_);
> > +	GEN5_IRQ_INIT(GEN8_PCU_);
> >  	POSTING_READ(GEN8_PCU_IIR);
> >  
> >  	ibx_irq_preinstall(dev);
> > -- 
> > 1.8.5.3
> > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ben Widawsky, Intel Open Source Technology Center
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

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