linux-kernel - Re: [PATCH v3 3/3] PCI: dwc: Enable MSI affinity support

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Message-ID: <b5e33957-1b8d-436b-888e-2b6f13d30782@nvidia.com>
Date: Tue, 27 Jan 2026 17:09:40 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Thomas Gleixner <tglx@...nel.org>, Radu Rendec <rrendec@...hat.com>,
 Manivannan Sadhasivam <mani@...nel.org>
Cc: Daniel Tsai <danielsftsai@...gle.com>, Marek Behún
 <kabel@...nel.org>, Krishna Chaitanya Chundru <quic_krichai@...cinc.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Wilczyński <kwilczynski@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Jingoo Han
 <jingoohan1@...il.com>, Brian Masney <bmasney@...hat.com>,
 Eric Chanudet <echanude@...hat.com>,
 Alessandro Carminati <acarmina@...hat.com>, Jared Kangas
 <jkangas@...hat.com>, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] PCI: dwc: Enable MSI affinity support

Hi Thomas,

On 27/01/2026 13:34, Thomas Gleixner wrote:
> On Tue, Jan 27 2026 at 11:30, Thomas Gleixner wrote:
>> The below untested hack should confirm that theory.
> 
> Actually looking at it deeper the solution is trivial because in this
> case writing the MSI message to the device is not required when the
> affinity changes because the message does not change. It is set once via
> msi_domain_activate() and stays the same for the life time of the
> interrupt.
> 
> So the below prevents the invocation of irq_chip_write_msi_msg() in
> msi_domain_set_affinity(), but I would recommend to investigate the
> actual underlying problem nevertheless:
> 
> It is going to roar its ugly head at some other place sooner than later
> as there are tons of other places which guard against
> pci_dev::current_state != PCI_D0.
> 
> Thanks,
> 
>          tglx
> ---
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -1495,7 +1495,7 @@ int irq_chip_redirect_set_affinity(struc
>   	WRITE_ONCE(redir->target_cpu, cpumask_first(dest));
>   	irq_data_update_effective_affinity(data, dest);
>   
> -	return IRQ_SET_MASK_OK;
> +	return IRQ_SET_MASK_OK_DONE;
>   }
>   EXPORT_SYMBOL_GPL(irq_chip_redirect_set_affinity);
>   #endif
> 

Yes that does fix it!

Tested-by: Jon Hunter <jonathanh@...dia.com>

Thanks!
Jon

-- 
nvpublic