linux-kernel - Re: [PATCH] PCI: dwc: Separate MSI out to different controller

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Message-ID: <CAK7fddDkQX1aj5ZyTjh1_Pk+XME3AY=m5ouEFRgmLuJjBJytbA@mail.gmail.com>
Date: Tue, 11 Feb 2025 16:23:53 +0800
From: Tsai Sung-Fu <danielsftsai@...gle.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Jingoo Han <jingoohan1@...il.com>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Krzysztof Wilczyński <kw@...ux.com>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Brian Norris <briannorris@...gle.com>, 
	Andrew Chant <achant@...gle.com>, Sajid Dalvi <sdalvi@...gle.com>
Subject: Re: [PATCH] PCI: dwc: Separate MSI out to different controller

>Because you cannot set affinity for chained MSIs as these MSIs are muxed to
>another parent interrupt. Since the IRQ affinity is all about changing which CPU
>gets the IRQ, affinity setting is only possible for the MSI parent.

So if we can find the MSI parent by making use of chained
relationships (32 MSI vectors muxed to 1 parent),
is it possible that we can add that implementation back ?
We have another patch that would like to add the
dw_pci_msi_set_affinity feature.
Would it be a possible try from your perspective ?

Thank you


On Tue, Feb 11, 2025 at 3:57 PM Manivannan Sadhasivam
<manivannan.sadhasivam@...aro.org> wrote:
>
> On Tue, Feb 11, 2025 at 03:16:11PM +0800, Tsai Sung-Fu wrote:
> > Hi Mani and Bjorn,
> >
> > Sorry for the late reply, we just found out some problems in the patch
> > we are trying to upstream here, and figuring out it might not be a
> > good idea to keep this process going, so I would drop this patch
> > submission, and come back once we figure it out a better way.
> >
> > BTW, May I ask why upstream chose to flag this driver with
> > MSI_FLAG_NO_AFFINITY and remove the function dw_pci_msi_set_affinity
> > implementation ?
> >
>
> Because you cannot set affinity for chained MSIs as these MSIs are muxed to
> another parent interrupt. Since the IRQ affinity is all about changing which CPU
> gets the IRQ, affinity setting is only possible for the MSI parent.
>
> - Mani
>
> --
> மணிவண்ணன் சதாசிவம்