linux-kernel - Re: [PATCH 0/2] PCI: Fix ACS enablement for Root Ports in DT platforms

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Message-ID: <tzlbsnsoymhjlri5rm7dw5btb2m2tpzemtyqhjpa2eu3josf5c@uivuvkpx3wep>
Date: Tue, 23 Sep 2025 21:07:49 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>, iommu@...ts.linux.dev,
        Anders Roxell <anders.roxell@...aro.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
        Xingang Wang <wangxingang5@...wei.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>, stable@...r.kernel.org
Subject: Re: [PATCH 0/2] PCI: Fix ACS enablement for Root Ports in DT
 platforms

On Thu, Sep 18, 2025 at 11:11:02AM -0300, Jason Gunthorpe wrote:
> On Wed, Sep 10, 2025 at 11:09:19PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > This issue was already found and addressed with a quirk for a different device
> > from Microsemi with 'commit, aa667c6408d2 ("PCI: Workaround IDT switch ACS
> > Source Validation erratum")'. Apparently, this issue seems to be documented in
> > the erratum #36 of IDT 89H32H8G3-YC, which is not publicly available.
> 
> This is a pretty broken device! I'm not sure this fix is good enough
> though.
> 
> For instance if you reset a downstream device it should loose its RID
> and then the config cycles waiting for reset to complete will trigger SV
> and reset will fail?
> 

No. Resetting the Ethernet controller connected to the switch downstream port
doesn't fail and we could see that the reset succeeds.

Maybe the bus number was still captured by the device.

> Maybe a better answer is to say these switches don't support SV and
> prevent the kernel from enabling it in the first place?
> 

I'm not sure though, as Windows seem to be running fine just with this erratum,
without disabling SV.

- Mani

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