linux-kernel - Re: [PATCH] Fix MSI-X with NIU cards

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Message-Id: <1242004911.7767.26.camel@concordia>
Date:	Mon, 11 May 2009 11:21:51 +1000
From:	Michael Ellerman <michael@...erman.id.au>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"David S. Miller" <davem@...emloft.net>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix MSI-X with NIU cards

On Fri, 2009-05-08 at 07:13 -0600, Matthew Wilcox wrote:
> The NIU device refuses to allow accesses to MSI-X registers before MSI-X
> is enabled.  This patch fixes the problem by moving the read of the mask
> register to after MSI-X is enabled.
> 
> Reported-by: David S. Miller <davem@...emloft.net>
> Tested-by: David S. Miller <davem@...emloft.net>
> Reviewed-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Matthew Wilcox <willy@...ux.intel.com>
> 
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index 6f2e629..3627732 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -455,8 +455,6 @@ static int msix_capability_init(struct pci_dev *dev,
>  		entry->msi_attrib.default_irq = dev->irq;
>  		entry->msi_attrib.pos = pos;
>  		entry->mask_base = base;
> -		entry->masked = readl(base + j * PCI_MSIX_ENTRY_SIZE +
> -					PCI_MSIX_ENTRY_VECTOR_CTRL_OFFSET);
>  		msix_mask_irq(entry, 1);

158 static void msix_mask_irq(struct msi_desc *desc, u32 flag)                  
159 {
160         u32 mask_bits = desc->masked;
...
165         writel(mask_bits, desc->mask_base + offset);


So I guess this device is just silently ignoring that write?

And aren't we violating the spec by writing 0x1 into the device there
(assuming desc->masked is 0x0 from the kzalloc), ie. we're supposed to
read and write back the reserved bits unchanged. (§ 6.8.2.9?)


> @@ -493,6 +491,12 @@ static int msix_capability_init(struct pci_dev *dev,
>  	msix_set_enable(dev, 1);
>  	dev->msix_enabled = 1;

Are we safe if we take an interrupt here?

> +	list_for_each_entry(entry, &dev->msi_list, list) {
> +		int vector = entry->msi_attrib.entry_nr;
> +		entry->masked = readl(base + vector * PCI_MSIX_ENTRY_SIZE +
> +					PCI_MSIX_ENTRY_VECTOR_CTRL_OFFSET);
> +	}
> +
>  	return 0;
>  }
>  

cheers


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