RE: [PATCH v2] PCI: imx6: Don't remove MSI capability For i.MX7D/i.MX8M

[Hongxing Zhu]

> -----Original Message-----
> From: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> Sent: 2026年3月30日 18:19
> To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> Cc: Frank Li <frank.li@xxxxxxx>; l.stach@xxxxxxxxxxxxxx;
> lpieralisi@xxxxxxxxxx; kwilczynski@xxxxxxxxxx; robh@xxxxxxxxxx;
> bhelgaas@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx;
> festevam@xxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxxxxxxx; Qiang Yu
> <qiang.yu@xxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v2] PCI: imx6: Don't remove MSI capability For
> i.MX7D/i.MX8M
> 
> On Mon, Mar 30, 2026 at 09:02:57AM +0000, Hongxing Zhu wrote:
> > > -----Original Message-----
> > > From: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> > > Sent: 2026年3月30日 15:23
> > > To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> > > Cc: Frank Li <frank.li@xxxxxxx>; l.stach@xxxxxxxxxxxxxx;
> > > lpieralisi@xxxxxxxxxx; kwilczynski@xxxxxxxxxx; robh@xxxxxxxxxx;
> > > bhelgaas@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx;
> kernel@xxxxxxxxxxxxxx;
> > > festevam@xxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> > > imx@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > stable@xxxxxxxxxxxxxxx; Qiang Yu <qiang.yu@xxxxxxxxxxxxxxxx>
> > > Subject: Re: [PATCH v2] PCI: imx6: Don't remove MSI capability For
> > > i.MX7D/i.MX8M
> > >
> > > + Qiang
> > >
> > > On Thu, Mar 19, 2026 at 05:18:23PM +0800, Richard Zhu wrote:
> > > > The MSI trigger mechanism for endpoint devices connected to
> > > > i.MX7D, i.MX8MM, and i.MX8MQ PCIe root complex ports depends on
> > > > the MSI capability register settings in the root complex. Removing
> > > > the MSI capability breaks MSI functionality for these endpoints.
> > > >
> > >
> > > What is the relation between Root Port MSI and endpoint MSI?
> > > Endpoint MSIs should be routed to the platform MSI controller (DWC
> > > i.MSI-RX or External like
> > > GIC-ITS) independent of the Root Port MSI state.
> > Hi Mani:
> > Thank for your kindly concern.
> > The MSI controller (DWC i.MSI-RX) on i.MX7D, i.MX8MM, and i.MX8MQ
> > platforms requires the RC's MSI capability to remain enabled. Removing
> > it breaks MSI routing from endpoints to the platform MSI controller.
> >
> 
> I understand that MSI is broken on your hardware, but I was trying to
> understand 'why' specifically. Because, Root Port MSI capability doesn't have
> anything to do with the endpoint MSIs. And since you mentioned that this
> issue happens only on one platform, could be that the hardware designers
> have mistakenly wired the Root Port's 'MSI Enable' to iMSI-RX's enable signal
> or something similar?
Yes, that makes sense. Based on the behavior we're seeing, it does appear to
be a hardware wiring issue specific to these platforms, possibly with the Root
Port's MSI Enable incorrectly connected to the iMSI-RX enable signal.
> 
> If so, we can introduce a flag 'dw_pcie_rp::keep_rp_msi_en' or something
> similar, set it for affected SoCs and skip the capability removal in
> pcie-designware-host.c
Good idea! I'll implement this approach with the 'dw_pcie_rp::keep_rp_msi_en' 
flag and skip the capability removal for affected SoCs in pcie-designware-host.c. 
Thanks for the suggestion!

Best Regards
Richard Zhu
> 
> - Mani
> 
> --
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