linux-kernel - Re: [PATCH V2] PCI/MSI: Set device flag indicating only 32-bit MSI support

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Date:   Thu, 3 Dec 2020 12:24:23 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vidya Sagar <vidyas@...dia.com>
Cc:     bhelgaas@...gle.com, lorenzo.pieralisi@....com,
        thierry.reding@...il.com, jonathanh@...dia.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V2] PCI/MSI: Set device flag indicating only 32-bit MSI
 support

On Tue, Nov 24, 2020 at 04:20:35PM +0530, Vidya Sagar wrote:
> There are devices (Ex:- Marvell SATA controller) that don't support
> 64-bit MSIs and the same is advertised through their MSI capability
> register. Set no_64bit_msi flag explicitly for such devices in the
> MSI setup code so that the msi_verify_entries() API would catch
> if the MSI arch code tries to use 64-bit MSI.

This seems good to me.  I'll post a possible revision to set
dev->no_64bit_msi in the device enumeration path instead of in the IRQ
allocation path, since it's really a property of the device, not of
the msi_desc.

I like the extra checking this gives us.  Was this prompted by
tripping over something, or is it something you noticed by code
reading?  If the former, a hint about what was wrong and how it's
being fixed would be useful.

> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
> ---
> V2:
> * Addressed Bjorn's comment and changed the error message
> 
>  drivers/pci/msi.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index d52d118979a6..8de5ba6b4a59 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -581,10 +581,12 @@ msi_setup_entry(struct pci_dev *dev, int nvec, struct irq_affinity *affd)
>  	entry->msi_attrib.multi_cap	= (control & PCI_MSI_FLAGS_QMASK) >> 1;
>  	entry->msi_attrib.multiple	= ilog2(__roundup_pow_of_two(nvec));
>  
> -	if (control & PCI_MSI_FLAGS_64BIT)
> +	if (control & PCI_MSI_FLAGS_64BIT) {
>  		entry->mask_pos = dev->msi_cap + PCI_MSI_MASK_64;
> -	else
> +	} else {
>  		entry->mask_pos = dev->msi_cap + PCI_MSI_MASK_32;
> +		dev->no_64bit_msi = 1;
> +	}
>  
>  	/* Save the initial mask status */
>  	if (entry->msi_attrib.maskbit)
> @@ -602,8 +604,9 @@ static int msi_verify_entries(struct pci_dev *dev)
>  	for_each_pci_msi_entry(entry, dev) {
>  		if (!dev->no_64bit_msi || !entry->msg.address_hi)
>  			continue;
> -		pci_err(dev, "Device has broken 64-bit MSI but arch"
> -			" tried to assign one above 4G\n");
> +		pci_err(dev, "Device has either broken 64-bit MSI or "
> +			"only 32-bit MSI support but "
> +			"arch tried to assign one above 4G\n");
>  		return -EIO;
>  	}
>  	return 0;
> -- 
> 2.17.1
>