linux-kernel - Re: [PATCH v4] PCI: xilinx-nwl: Fix Multi MSI data programming

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Date:   Wed, 12 Jun 2019 17:31:20 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        bhelgaas@...gle.com, linux-arm-kernel@...ts.infradead.org,
        rgummal@...inx.com
Subject: Re: [PATCH v4] PCI: xilinx-nwl: Fix Multi MSI data programming

On Wed, Jun 12, 2019 at 02:01:56PM +0100, Marc Zyngier wrote:
> On Wed, 12 Jun 2019 11:17:59 +0100,
> Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com> wrote:
> > 
> > The current Multi MSI data programming fails if multiple end points
> > requesting MSI and multi MSI are connected with switch, i.e the current
> > multi MSI data being given is not considering the number of vectors
> > being requested in case of multi MSI.
> > Ex: Two EP's connected via switch, EP1 requesting single MSI first,
> > EP2 requesting Multi MSI of count four. The current code gives
> > MSI data 0x0 to EP1 and 0x1 to EP2, but EP2 can modify lower two bits
> > due to which EP2 also sends interrupt with MSI data 0x0 which results
> > in always invoking virq of EP1 due to which EP2 MSI interrupt never
> > gets handled.
> 
> I think there is a much simpler explanation for this: Multi-MSI
> mandates that the base interrupt number is naturally aligned to its
> size. Having switches in the middle is just a way to expose the issue,
> but you could see it failing with a single end-point and two MSIs that
> are assigned on an odd boundary.

Agreed, I will rewrite the commit log with a link to the specs,
a switch has no role to play in this bug.

Lorenzo

> > Fix Multi MSI data programming with required alignment by
> > using number of vectors being requested.
> > 
> > Fixes: ab597d35ef11 ("PCI: xilinx-nwl: Add support for Xilinx NWL PCIe
> > Host Controller")
> > 
> > Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
> > ---
> > V4:
> >  - Using a different bitmap registration API whcih serves single and multi
> >    MSI requests.
> > ---
> >  drivers/pci/controller/pcie-xilinx-nwl.c | 11 +++++------
> >  1 file changed, 5 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pcie-xilinx-nwl.c b/drivers/pci/controller/pcie-xilinx-nwl.c
> > index 81538d7..a9e07b8 100644
> > --- a/drivers/pci/controller/pcie-xilinx-nwl.c
> > +++ b/drivers/pci/controller/pcie-xilinx-nwl.c
> > @@ -483,15 +483,13 @@ static int nwl_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
> >  	int i;
> >  
> >  	mutex_lock(&msi->lock);
> > -	bit = bitmap_find_next_zero_area(msi->bitmap, INT_PCI_MSI_NR, 0,
> > -					 nr_irqs, 0);
> > -	if (bit >= INT_PCI_MSI_NR) {
> > +	bit = bitmap_find_free_region(msi->bitmap, INT_PCI_MSI_NR,
> > +				      get_count_order(nr_irqs));
> > +	if (bit < 0) {
> >  		mutex_unlock(&msi->lock);
> >  		return -ENOSPC;
> >  	}
> >  
> > -	bitmap_set(msi->bitmap, bit, nr_irqs);
> > -
> >  	for (i = 0; i < nr_irqs; i++) {
> >  		irq_domain_set_info(domain, virq + i, bit + i, &nwl_irq_chip,
> >  				domain->host_data, handle_simple_irq,
> > @@ -509,7 +507,8 @@ static void nwl_irq_domain_free(struct irq_domain *domain, unsigned int virq,
> >  	struct nwl_msi *msi = &pcie->msi;
> >  
> >  	mutex_lock(&msi->lock);
> > -	bitmap_clear(msi->bitmap, data->hwirq, nr_irqs);
> > +	bitmap_release_region(msi->bitmap, data->hwirq,
> > +			      get_count_order(nr_irqs));
> >  	mutex_unlock(&msi->lock);
> >  }
> >  
> > -- 
> > 2.7.4
> > 
> 
> As for the body of the patch:
> 
> Suggested-by: Marc Zyngier <marc.zyngier@....com>
> Acked-by: Marc Zyngier <marc.zyngier@....com>
> 
> Thanks,
> 
> 	M.
> 
> -- 
> Jazz is not dead, it just smells funny.