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

[Frank Li]

On Fri, Mar 27, 2026 at 08:12:29AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Frank Li <frank.li@xxxxxxx>
> > Sent: 2026年3月19日 22:17
> > To: Hongxing Zhu <hongxing.zhu@xxxxxxx>
> > Cc: l.stach@xxxxxxxxxxxxxx; lpieralisi@xxxxxxxxxx; kwilczynski@xxxxxxxxxx;
> > mani@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
> > Subject: Re: [PATCH v2] PCI: imx6: Don't remove MSI capability For
> > i.MX7D/i.MX8M
> >
> > 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.
> > >
> > > Preserve the MSI capability for i.MX7D/i.MX8M PCIe root complex to
> > > maintain MSI functionality.
> > >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Fixes: f5cd8a929c825 ("PCI: dwc: Remove MSI/MSIX capability for Root
> > > Port if iMSI-RX is used as MSI controller")
> >
> > I think it'd better add another varible to check in f5cd8a929c825 if
> > (pp->has_msi_ctrl && !pp->xxx_broken) or direct use IP version, which
> > already auto detected.
> >
> > Previous patch have not consider this old version controller.
> Hi Frank:
> From what I've observed, this behavior seems tied to the specific controller
> design. For example, neither the i.MX6Q nor the i.MX6SX exhibit this issue.

Yes, should rename has_msi_ctrl -> disable_msi_ctrl. Set it according to
difference condition, such as has_msi_ctrl or skip it for problem platform
such as i.MX8MM and i.MX8MQ.

Disable it and overwrite later will cause confuse.

>
> The intention of commit f5cd8a929c825 is to remove the MSI capability from the
> Root Complex (RC). From the author's perspective, this change should not
> affect the  Endpoint's (EP) MSI functionality.

Yes, your patch fix  RC  mode?

Frank
>
> I'm not sure do this check (pp->has_msi_ctrl && !pp->msi_broken) is proper or not.
> Best Regards
> Richard Zhu
> > >