linux-kernel - Re: [PATCH 2/2] PCI: iproc: Support multi-MSI only on uniprocessor kernel

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Date:   Mon, 7 Jun 2021 09:48:21 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Sandor Bodo-Merle <sbodomerle@...il.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH 2/2] PCI: iproc: Support multi-MSI only on uniprocessor
 kernel



On 6/6/2021 5:30 AM, Sandor Bodo-Merle wrote:
> The interrupt affinity scheme used by this driver is incompatible with
> multi-MSI as it implies moving the doorbell address to that of another MSI
> group.  This isn't possible for multi-MSI, as all the MSIs must have the
> same doorbell address. As such it is restricted to systems with a single
> CPU.
> 
> Fixes: fc54bae28818 ("PCI: iproc: Allow allocation of multiple MSIs")
> Reported-by: Marc Zyngier <maz@...nel.org>
> Signed-off-by: Sandor Bodo-Merle <sbodomerle@...il.com>
> ---
>  drivers/pci/controller/pcie-iproc-msi.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-iproc-msi.c b/drivers/pci/controller/pcie-iproc-msi.c
> index 557d93dcb3bc..81b4effeb130 100644
> --- a/drivers/pci/controller/pcie-iproc-msi.c
> +++ b/drivers/pci/controller/pcie-iproc-msi.c
> @@ -171,7 +171,7 @@ static struct irq_chip iproc_msi_irq_chip = {
>  
>  static struct msi_domain_info iproc_msi_domain_info = {
>  	.flags = MSI_FLAG_USE_DEF_DOM_OPS | MSI_FLAG_USE_DEF_CHIP_OPS |
> -		MSI_FLAG_MULTI_PCI_MSI | MSI_FLAG_PCI_MSIX,
> +		MSI_FLAG_PCI_MSIX,
>  	.chip = &iproc_msi_irq_chip,
>  };
>  
> @@ -250,6 +250,9 @@ static int iproc_msi_irq_domain_alloc(struct irq_domain *domain,
>  	struct iproc_msi *msi = domain->host_data;
>  	int hwirq, i;
>  
> +	if (msi->nr_cpus > 1 && nr_irqs > 1)
> +		return -EINVAL;
> +

This should never happen since the framework would have guarded against
this. But I guess it does not hurt to have the check here.

>  	mutex_lock(&msi->bitmap_lock);
>  
>  	/*
> @@ -540,6 +543,9 @@ int iproc_msi_init(struct iproc_pcie *pcie, struct device_node *node)
>  	mutex_init(&msi->bitmap_lock);
>  	msi->nr_cpus = num_possible_cpus();
>  
> +	if (msi->nr_cpus == 1)
> +		iproc_msi_domain_info.flags |=  MSI_FLAG_MULTI_PCI_MSI;
> +
>  	msi->nr_irqs = of_irq_count(node);
>  	if (!msi->nr_irqs) {
>  		dev_err(pcie->dev, "found no MSI GIC interrupt\n");
> 

Looks fine to me. Thanks.

Acked-by: Ray Jui <ray.jui@...adcom.com>

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