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

From: Bjorn Helgaas <helgaas@kernel.org>
To: Vidya Sagar <vidyas@nvidia.com>
Cc: bhelgaas@google.com, lorenzo.pieralisi@arm.com,
	thierry.reding@gmail.com, jonathanh@nvidia.com,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	kthota@nvidia.com, mmaddireddy@nvidia.com, sagar.tv@gmail.com
Subject: Re: [PATCH] PCI/MSI: Set device flag indicating only 32-bit MSI support
Date: Fri, 20 Nov 2020 15:30:36 -0600	[thread overview]
Message-ID: <20201120213036.GA278887@bjorn-Precision-5520> (raw)
In-Reply-To: <20201117145728.4516-1-vidyas@nvidia.com>

On Tue, Nov 17, 2020 at 08:27:28PM +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. 

I *think* you're saying these devices behave correctly per spec: they
don't support 64-bit MSI, and they don't advertise support for 64-bit
MSI.  Right?

> 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.

And you want msi_verify_entries() to catch attempts by the arch code
to assign a 64-bit MSI address?

That sounds OK, but the error message ("Device has broken 64-bit MSI")
is not appropriate if the device is actually *not* broken.

> Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> ---
>  drivers/pci/msi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index d52d118979a6..af49da28854e 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)
> -- 
> 2.17.1
> 