Re: [RFC PATCH 1/5] iommu/arm-smmu-v3: Refactor arm_smmu_setup_irqs

[Pranjal Shrivastava <praan@google.com>]

On Tue, Mar 18, 2025 at 09:50:16PM -0700, Nicolin Chen wrote:
> On Wed, Mar 19, 2025 at 12:42:50AM +0000, Pranjal Shrivastava wrote:
> > Refactor arm_smmu_setup_irqs by splitting it into two parts, one for
> > registering interrupt handlers and the other one for enabling interrupt
> > generation in the hardware. This refactor helps in re-initialization of
> > hardware interrupts as part of a subsequent patch that enables runtime
> > power management for the arm-smmu-v3 driver.
> > 
> > Signed-off-by: Pranjal Shrivastava <praan@google.com>
> > ---
> >  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 50 ++++++++++++++++-----
> >  1 file changed, 38 insertions(+), 12 deletions(-)
> 
> > +static int arm_smmu_setup_irqs(struct arm_smmu_device *smmu)
> > +{
> > +	int ret, irq;
> > +
> > +	/* Disable IRQs first */
> > +	ret = arm_smmu_disable_irqs(smmu);
> 
> Why do we need to touch HW in this SW handler setting-up function?
> 

This is just to maintain status quo, if you look at the current
`arm_smmu_setup_irqs` we still:

	/* Disable IRQs first */
	ret = arm_smmu_write_reg_sync(smmu, 0,ARM_SMMU_IRQ_CTRL,
				      ARM_SMMU_IRQ_CTRLACK);


> > @@ -4171,6 +4187,9 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu)
> >  		return ret;
> >  	}
> >  
> > +	/* Enable interrupt generation on the SMMU */
> > +	arm_smmu_enable_irqs(smmu);
> > +
> 
> Should this replace arm_smmu_setup_irqs() in this function? I see
> arm_smmu_setup_irqs() still remain in arm_smmu_device_reset(), so
> a normal probe routine would call it twice?
> 
> In my view, arm_smmu_setup_irqs() can be done just once, moving
> out of arm_smmu_device_reset() and up to arm_smmu_device_probe()?
> 

That makes sense, I kept the `arm_smmu_setup_irqs()` here to re-init the
MSIs during resume but I guess it's better to call `arm_smmu_setup_irqs`
once during probe and maybe re-work to call `arm_smmu_setup_msis` during
resume to re-alloc the MSIs. I'll add this in the next version.

Thanks,
Praan