linux-kernel - Re: [PATCH] PCI/MSI: Initialize the prepare descriptor by default

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Message-ID: <34d1f7e4-0729-4faf-95b7-e2fce6c3be2e@linux.microsoft.com>
Date: Wed, 9 Jul 2025 10:12:09 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Shradha Gupta <shradhagupta@...ux.microsoft.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Thomas Gleixner <tglx@...utronix.de>,
 Marc Zyngier <maz@...nel.org>, Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Shivamurthy Shastri <shivamurthy.shastri@...utronix.de>,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hyperv@...r.kernel.org, Roman Kisel <romank@...ux.microsoft.com>
Subject: Re: [PATCH] PCI/MSI: Initialize the prepare descriptor by default



On 7/8/2025 9:38 PM, Bjorn Helgaas wrote:
> On Tue, Jul 08, 2025 at 03:45:05PM +0530, Naman Jain wrote:
>> On 7/8/2025 3:32 PM, Shradha Gupta wrote:
>>> On Tue, Jul 08, 2025 at 10:48:48AM +0530, Naman Jain wrote:
>>>> Plug the default MSI-X prepare descriptor for non-implemented ops by
>>>> default to workaround the inability of Hyper-V vPCI module to setup
>>>> the MSI-X descriptors properly; especially for dynamically allocated
>>>> MSI-X.
>>>>
>>>> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
>>>> ---
>>>>    drivers/pci/msi/irqdomain.c | 2 ++
>>>>    1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
>>>> index 765312c92d9b..655e99b9c8cc 100644
>>>> --- a/drivers/pci/msi/irqdomain.c
>>>> +++ b/drivers/pci/msi/irqdomain.c
>>>> @@ -84,6 +84,8 @@ static void pci_msi_domain_update_dom_ops(struct msi_domain_info *info)
>>>>    	} else {
>>>>    		if (ops->set_desc == NULL)
>>>>    			ops->set_desc = pci_msi_domain_set_desc;
>>>> +		if (ops->prepare_desc == NULL)
>>>> +			ops->prepare_desc = pci_msix_prepare_desc;
>>>>    	}
>>>>    }
>>>>
>>>> base-commit: 26ffb3d6f02cd0935fb9fa3db897767beee1cb2a
>>>> -- 
>>>> 2.34.1
>>>>
>>>
>>> Hey Naman,
>>>
>>> can you please try your tests with this patch:
>>> https://lore.kernel.org/all/1749651015-9668-1-git-send-email-shradhagupta@linux.microsoft.com/
>>> I think this should help your use case
>>
>> Hey,
>> Thanks for sharing this, this works for me.
>>
>> Closing this thread.
> 
> I guess this means we should ignore this patch?  If it turns out that
> we do need this patch, I'd like to add some details in the commit log
> about what this problem looks like to users.
> 
> Bjorn

Yes, my patch is no longer required, since it was doing the same thing
that Shradha's patch (1-2) were doing, but in a different way. Shradha's
patch is better and would suffice for the use case. Please ignore this
patch.

Thanks.
Regards,
Naman