Re: [Intel-gfx] [PATCH 06/18] drm/i915/guc: Drop guc->interrupts.enabled

From: Matthew Brost <matthew.brost@intel.com>
To: John Harrison <john.c.harrison@intel.com>
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH 06/18] drm/i915/guc: Drop guc->interrupts.enabled
Date: Thu, 27 May 2021 10:13:55 -0700	[thread overview]
Message-ID: <20210527171354.GA12785@sdutt-i7> (raw)
In-Reply-To: <3b1eadf8-b043-365f-ada9-3a87901e8159@intel.com>

On Thu, May 27, 2021 at 10:17:20AM -0700, John Harrison wrote:
> On 5/25/2021 23:42, Matthew Brost wrote:
> > Drop the variable guc->interrupts.enabled as this variable is just
> > leading to bugs creeping into the code.
> > 
> > e.g. A full GPU reset disables the GuC interrupts but forgot to clear
> > guc->interrupts.enabled, guc->interrupts.enabled being true suppresses
> > interrupts from getting re-enabled and now we are broken.
> > 
> > It is harmless to enable interrupt while already enabled so let's just
> > delete this variable to avoid bugs like this going forward.
> Is it worth leaving the enabled flag in place but only using it to trip a
> WARN to catch such cases in a less catastrophic manner? Or are there valid
> reasons for calling enable when already enabled?
>

I don't think so as mentioned above a reset disables these interrupts
and if we didn't clear this field the WARN_ON would be triggered making
CI unhappy. Yes, the bug would less catastrophic but we'd still have to
waste time and energy chasing it.

Matt 

> Either way, it seems like a plausible change and CI is happy with it, so:
> Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
> 
> John.
> 
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/uc/intel_guc.c | 27 +++++++++-----------------
> >   drivers/gpu/drm/i915/gt/uc/intel_guc.h |  1 -
> >   2 files changed, 9 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.c b/drivers/gpu/drm/i915/gt/uc/intel_guc.c
> > index ab2c8fe8cdfa..18da9ed15728 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.c
> > @@ -96,12 +96,9 @@ static void gen9_enable_guc_interrupts(struct intel_guc *guc)
> >   	assert_rpm_wakelock_held(&gt->i915->runtime_pm);
> >   	spin_lock_irq(&gt->irq_lock);
> > -	if (!guc->interrupts.enabled) {
> > -		WARN_ON_ONCE(intel_uncore_read(gt->uncore, GEN8_GT_IIR(2)) &
> > -			     gt->pm_guc_events);
> > -		guc->interrupts.enabled = true;
> > -		gen6_gt_pm_enable_irq(gt, gt->pm_guc_events);
> > -	}
> > +	WARN_ON_ONCE(intel_uncore_read(gt->uncore, GEN8_GT_IIR(2)) &
> > +		     gt->pm_guc_events);
> > +	gen6_gt_pm_enable_irq(gt, gt->pm_guc_events);
> >   	spin_unlock_irq(&gt->irq_lock);
> >   }
> > @@ -112,7 +109,6 @@ static void gen9_disable_guc_interrupts(struct intel_guc *guc)
> >   	assert_rpm_wakelock_held(&gt->i915->runtime_pm);
> >   	spin_lock_irq(&gt->irq_lock);
> > -	guc->interrupts.enabled = false;
> >   	gen6_gt_pm_disable_irq(gt, gt->pm_guc_events);
> > @@ -134,18 +130,14 @@ static void gen11_reset_guc_interrupts(struct intel_guc *guc)
> >   static void gen11_enable_guc_interrupts(struct intel_guc *guc)
> >   {
> >   	struct intel_gt *gt = guc_to_gt(guc);
> > +	u32 events = REG_FIELD_PREP(ENGINE1_MASK, GUC_INTR_GUC2HOST);
> >   	spin_lock_irq(&gt->irq_lock);
> > -	if (!guc->interrupts.enabled) {
> > -		u32 events = REG_FIELD_PREP(ENGINE1_MASK, GUC_INTR_GUC2HOST);
> > -
> > -		WARN_ON_ONCE(gen11_gt_reset_one_iir(gt, 0, GEN11_GUC));
> > -		intel_uncore_write(gt->uncore,
> > -				   GEN11_GUC_SG_INTR_ENABLE, events);
> > -		intel_uncore_write(gt->uncore,
> > -				   GEN11_GUC_SG_INTR_MASK, ~events);
> > -		guc->interrupts.enabled = true;
> > -	}
> > +	WARN_ON_ONCE(gen11_gt_reset_one_iir(gt, 0, GEN11_GUC));
> > +	intel_uncore_write(gt->uncore,
> > +			   GEN11_GUC_SG_INTR_ENABLE, events);
> > +	intel_uncore_write(gt->uncore,
> > +			   GEN11_GUC_SG_INTR_MASK, ~events);
> >   	spin_unlock_irq(&gt->irq_lock);
> >   }
> > @@ -154,7 +146,6 @@ static void gen11_disable_guc_interrupts(struct intel_guc *guc)
> >   	struct intel_gt *gt = guc_to_gt(guc);
> >   	spin_lock_irq(&gt->irq_lock);
> > -	guc->interrupts.enabled = false;
> >   	intel_uncore_write(gt->uncore, GEN11_GUC_SG_INTR_MASK, ~0);
> >   	intel_uncore_write(gt->uncore, GEN11_GUC_SG_INTR_ENABLE, 0);
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > index c20f3839de12..4abc59f6f3cd 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
> > @@ -33,7 +33,6 @@ struct intel_guc {
> >   	unsigned int msg_enabled_mask;
> >   	struct {
> > -		bool enabled;
> >   		void (*reset)(struct intel_guc *guc);
> >   		void (*enable)(struct intel_guc *guc);
> >   		void (*disable)(struct intel_guc *guc);
> 
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