RE: [PATCH v2] PCI: imx6: Keep Root Port MSI capability also for i.MX6Q

[Hongxing Zhu]

> -----Original Message-----
> From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
> Sent: Friday, July 17, 2026 6:27 AM
> To: Soeren Moch <smoch@xxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; stable@xxxxxxxxxxxxxxx; Hongxing
> Zhu <hongxing.zhu@xxxxxxx>; Frank Li <frank.li@xxxxxxx>; Manivannan
> Sadhasivam <mani@xxxxxxxxxx>; Lucas Stach <l.stach@xxxxxxxxxxxxxx>; Fabio
> Estevam <festevam@xxxxxxxxx>; linux-pci@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] PCI: imx6: Keep Root Port MSI capability also for i.MX6Q
> 
> On Thu, Jul 16, 2026 at 11:40:54PM +0200, Soeren Moch wrote:
> > On the NXP i.MX6Q chipset MSIs from the endpoints won't be received by
> > the iMSI-RX MSI controller if the Root Port MSI capability is disabled.
> >
> > Even though the Root Port MSIs won't be received by the iMSI-RX
> > controller due to design, this chipset has some weird hardware bug
> > that prevents the endpoint MSIs from reaching when the Root Port MSI
> > capability is disabled.
> >
> > Hence, always keep the Root Port MSI capability for this chipset.
> >
> > Note that by keeping Root Port MSI capability, Root Port MSIs such as
> > AER, PME and others won't be received by default. So users need to use
> > workarounds such as passing 'pcie_pme=nomsi' cmdline param.
> 
> I'd like to align the subject a little more with 3a4e8302e72f and avoid repeating
> the ".. from reaching when the Root Port MSI ..." part of the commit log, which
> seems to be missing a word.  So I propose the following (if you think it's accurate):
> 
>   PCI: imx6: Keep i.MX6Q Root Port MSI capability with iMSI-RX to work around
> hardware bug
> 
>   On some NXP chipsets, disabling Root Port MSI/MSI-X Capabilities blocks
>   MSIs originating from Endpoints from reaching the iMSI-RX controller.
> 
>   To address this hardware bug, 3a4e8302e72f ("PCI: imx6: Keep Root Port MSI
>   capability with iMSI-RX to work around hardware bug") preserves Root Port
>   MSI and MSI-X Capabilities on i.MX7D, i.MX8MM, and i.MX8MQ when iMSI-RX
> is
>   in use.
> 
>   The same applies to i.MX6Q, so preserve Root Port MSI/MSI-X Capabilities
>   there as well.
> 
>   Note that preserving these Capabilities means Root Port-originated MSIs
>   such as AER and PME won't be received due to separate hardware limitations.
>   Users may need to use workarounds such as passing the 'pcie_pme=nomsi'
>   command-line parameter.
> 
> Also, we need to resolve the Sashiko question about whether IMX6QP and
> IMX6SX also need this.  NXP folks, can you verify?
Hi Bjorn:
Thank you for the reminder.

You are correct. I apologize for not covering these legacy platforms
initially. I have now verified that i.MX6QP and i.MX6SX PCIe controllers have
the same issue, so the fix should be applied to these platforms as well.

Should I send a separate patch for i.MX6QP and i.MX6SX, or would you prefer
that I extend this commit to cover all three variants in v3?

Best Regards
Richard Zhu
> 
> > Fixes: f5cd8a929c825 ("PCI: dwc: Remove MSI/MSIX capability for Root
> > Port if iMSI-RX is used as MSI controller")
> > Cc: <stable@xxxxxxxxxxxxxxx> # 7.0+
> > Signed-off-by: Soeren Moch <smoch@xxxxxx>
> > Acked-by: Richard Zhu <hongxing.zhu@xxxxxxx>
> > Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> > Reviewed-by: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> > ---
> > Cc: Manivannan Sadhasivam <mani@xxxxxxxxxx>
> > Cc: Richard Zhu <hongxing.zhu@xxxxxxx>
> > Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > Cc: Frank Li <Frank.Li@xxxxxxx>
> > Cc: Fabio Estevam <festevam@xxxxxxxxx>
> > Cc: linux-pci@xxxxxxxxxxxxxxx
> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > Cc: imx@xxxxxxxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> >
> > This patch is similar to
> > 3a4e8302e72f ("PCI: imx6: Keep Root Port MSI capability with iMSI-RX
> > to work around hardware bug")
> >
> > Tested on a tbs2910 board [1]
> > [1] arch/arm/boot/dts/nxp/imx/imx6q-tbs2910.dts
> >
> > changes in v2:
> > - collect a-b and r-b tags
> > - use correct fixes tag (Manivannan)
> >   (reference commit that introduced the bug, not the incomplete fix)
> >
> > Since this is a fix for a regression in linux-7.0+, can this still be merged for 7.2-
> rcS ?
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 98e1db751132..8130cf93c2bb 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -1995,7 +1995,8 @@ static const struct imx_pcie_drvdata drvdata[] = {
> >  		.flags = IMX_PCIE_FLAG_IMX_PHY |
> >  			 IMX_PCIE_FLAG_SPEED_CHANGE_WORKAROUND |
> >  			 IMX_PCIE_FLAG_BROKEN_SUSPEND |
> > -			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND,
> > +			 IMX_PCIE_FLAG_SUPPORTS_SUSPEND |
> > +			 IMX_PCIE_FLAG_KEEP_MSI_CAP,
> >  		.dbi_length = 0x200,
> >  		.gpr = "fsl,imx6q-iomuxc-gpr",
> >  		.ltssm_off = IOMUXC_GPR12,
> > --
> > 2.43.0
> >