Re: [PATCH 08/12] PCI: xgene-msi: Get rid of intermediate tracking structure

[Marc Zyngier <maz@kernel.org>]

On Mon, 07 Jul 2025 16:22:43 +0100,
Lorenzo Pieralisi <lpieralisi@kernel.org> wrote:
> 
> On Sat, Jun 28, 2025 at 06:30:01PM +0100, Marc Zyngier wrote:
> > The xgene-msi driver uses an odd construct in the form of an
> > intermediate tracking structure, evidently designed to deal with
> > multiple instances of the MSI widget. However, the existing HW
> > only has one set, and it is obvious that there won't be new HW
> > coming down that particular line.
> > 
> > Simplify the driver by using a bit of pointer arithmetic instead,
> > directly tracking the interrupt and avoiding extra memory allocation.
> 
> A couple of nits, nothing else.
> 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  drivers/pci/controller/pci-xgene-msi.c | 58 ++++++++------------------
> >  1 file changed, 17 insertions(+), 41 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pci-xgene-msi.c b/drivers/pci/controller/pci-xgene-msi.c
> > index b3ac0125b3b40..4be79b9ff80df 100644
> > --- a/drivers/pci/controller/pci-xgene-msi.c
> > +++ b/drivers/pci/controller/pci-xgene-msi.c
> > @@ -24,19 +24,13 @@
> >  #define NR_HW_IRQS		16
> >  #define NR_MSI_VEC		(IDX_PER_GROUP * IRQS_PER_IDX * NR_HW_IRQS)
> >  
> > -struct xgene_msi_group {
> > -	struct xgene_msi	*msi;
> > -	int			gic_irq;
> > -	u32			msi_grp;
> > -};
> > -
> >  struct xgene_msi {
> >  	struct irq_domain	*inner_domain;
> >  	u64			msi_addr;
> >  	void __iomem		*msi_regs;
> >  	unsigned long		*bitmap;
> >  	struct mutex		bitmap_lock;
> > -	struct xgene_msi_group	*msi_groups;
> > +	unsigned int		gic_irq[NR_HW_IRQS];
> >  };
> >  
> >  /* Global data */
> > @@ -261,27 +255,20 @@ static int xgene_msi_init_allocator(struct device *dev)
> >  
> >  	mutex_init(&xgene_msi_ctrl->bitmap_lock);
> >  
> > -	xgene_msi_ctrl->msi_groups = devm_kcalloc(dev, NR_HW_IRQS,
> > -						  sizeof(struct xgene_msi_group),
> > -						  GFP_KERNEL);
> > -	if (!xgene_msi_ctrl->msi_groups)
> > -		return -ENOMEM;
> > -
> >  	return 0;
> >  }
> >  
> >  static void xgene_msi_isr(struct irq_desc *desc)
> >  {
> > +	unsigned int *irqp = irq_desc_get_handler_data(desc);
> >  	struct irq_chip *chip = irq_desc_get_chip(desc);
> >  	struct xgene_msi *xgene_msi = xgene_msi_ctrl;
> > -	struct xgene_msi_group *msi_groups;
> >  	int msir_index, msir_val, hw_irq, ret;
> >  	u32 intr_index, grp_select, msi_grp;
> >  
> >  	chained_irq_enter(chip, desc);
> >  
> > -	msi_groups = irq_desc_get_handler_data(desc);
> > -	msi_grp = msi_groups->msi_grp;
> > +	msi_grp = irqp - xgene_msi->gic_irq;
> >  
> >  	/*
> >  	 * MSIINTn (n is 0..F) indicates if there is a pending MSI interrupt
> > @@ -341,35 +328,31 @@ static void xgene_msi_remove(struct platform_device *pdev)
> >  		cpuhp_remove_state(pci_xgene_online);
> >  	cpuhp_remove_state(CPUHP_PCI_XGENE_DEAD);
> >  
> > -	kfree(msi->msi_groups);
> > -
> >  	xgene_free_domains(msi);
> >  }
> >  
> >  static int xgene_msi_hwirq_alloc(unsigned int cpu)
> >  {
> > -	struct xgene_msi *msi = xgene_msi_ctrl;
> > -	struct xgene_msi_group *msi_group;
> >  	int i;
> >  	int err;
> >  
> >  	for (i = cpu; i < NR_HW_IRQS; i += num_possible_cpus()) {
> > -		msi_group = &msi->msi_groups[i];
> > +		unsigned int irq = xgene_msi_ctrl->gic_irq[i];
> >  
> >  		/*
> >  		 * Statically allocate MSI GIC IRQs to each CPU core.
> >  		 * With 8-core X-Gene v1, 2 MSI GIC IRQs are allocated
> >  		 * to each core.
> >  		 */
> > -		irq_set_status_flags(msi_group->gic_irq, IRQ_NO_BALANCING);
> > -		err = irq_set_affinity(msi_group->gic_irq, cpumask_of(cpu));
> > +		irq_set_status_flags(irq, IRQ_NO_BALANCING);
> > +		err = irq_set_affinity(irq, cpumask_of(cpu));
> >  		if (err) {
> >  			pr_err("failed to set affinity for GIC IRQ");
> >  			return err;
> >  		}
> >  
> > -		irq_set_chained_handler_and_data(msi_group->gic_irq,
> > -			xgene_msi_isr, msi_group);
> > +		irq_set_chained_handler_and_data(irq, xgene_msi_isr,
> > +						 &xgene_msi_ctrl->gic_irq[i]);
> >  	}
> >  
> >  	return 0;
> > @@ -378,15 +361,12 @@ static int xgene_msi_hwirq_alloc(unsigned int cpu)
> >  static int xgene_msi_hwirq_free(unsigned int cpu)
> >  {
> >  	struct xgene_msi *msi = xgene_msi_ctrl;
> > -	struct xgene_msi_group *msi_group;
> >  	int i;
> >  
> >  	for (i = cpu; i < NR_HW_IRQS; i += num_possible_cpus()) {
> > -		msi_group = &msi->msi_groups[i];
> > -		if (!msi_group->gic_irq)
> > +		if (!msi->gic_irq[i])
> 
> In patch 5 we removed this check in xgene_msi_hwirq_alloc(), if it
> superfluous there it should be here too.

Hmmm, good point. I'll get rid of that one too.

> 
> >  			continue;
> > -		irq_set_chained_handler_and_data(msi_group->gic_irq, NULL,
> > -						 NULL);
> > +		irq_set_chained_handler_and_data(msi->gic_irq[i], NULL, NULL);
> >  	}
> >  	return 0;
> >  }
> > @@ -399,10 +379,9 @@ static const struct of_device_id xgene_msi_match_table[] = {
> >  static int xgene_msi_probe(struct platform_device *pdev)
> >  {
> >  	struct resource *res;
> > -	int rc, irq_index;
> 
> Just noticed, insignificant nit: don't see why moving irq_index to a
> local loop variable is required in this patch - fine to leave the
> code in the patch as-is - reporting it to make sure I have not
> missed anything.

Not required, just my own obsession with scope reduction of local
variables. I thought that given the magnitude of the changes, I might
as well give myself some artistic license! ;-)

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.