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

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Message-ID: <86r27zarej.wl-marc.zyngier@arm.com>
Date:   Wed, 12 Jun 2019 14:01:56 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
Cc:     <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <lorenzo.pieralisi@....com>, <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, 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.

> 
> 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.