RE: [PATCH v1] PCI: imx6: Enable L1SS support when supports_clkreq is true

[Hongxing Zhu (OSS)]

> -----Original Message-----
> From: Fabio Estevam <festevam@xxxxxxxxx>
> Sent: Friday, November 6, 2026 8:11 PM
> To: Hongxing Zhu (OSS) <hongxing.zhu@xxxxxxxxxxx>
> Cc: Frank Li (OSS) <frank.li@xxxxxxxxxxx>; jingoohan1@xxxxxxxxx;
> l.stach@xxxxxxxxxxxxxx; lpieralisi@xxxxxxxxxx; kwilczynski@xxxxxxxxxx;
> mani@xxxxxxxxxx; robh@xxxxxxxxxx; bhelgaas@xxxxxxxxxx;
> s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Hongxing Zhu <hongxing.zhu@xxxxxxx>
> Subject: Re: [PATCH v1] PCI: imx6: Enable L1SS support when supports_clkreq
> is true
> 
> On Fri, Nov 6, 2026 at 6:00 AM <hongxing.zhu@xxxxxxxxxxx> wrote:
> >
> > From: Richard Zhu <hongxing.zhu@xxxxxxx>
> >
> > Add support L1SS support for the i.MX6 PCIe controller when the
> > `supports_clkreq` flag is set.
> 
> Please explain why this is needed.
> 
> Also, does it need a Fixes tag? 
Hi Fabio:
Thanks for your comments.
The change is intended to enable L1SS for the i.MX6 PCIe controller when the
supports_clkreq flag is set.

The commit a00bba406b5a ("PCI: dwc: Advertise L1 PM Substates only if driver
requests it") introduced a mechanism that clears the L1SS capabilities by
default. However, the i.MX PCIe controller inherently supports L1SS, as
indicated by the settings in the L1SS capabilities register.

By setting dw_pcie.l1ss_support to true when supports_clkreq is true, we
ensure that the i.MX6 PCIe controller can properly utilize L1SS, allowing the
PCIe endpoint to enter low-power states efficiently when the link is not in
use. This optimization is crucial for power management and energy efficiency
on i.MX6-based platforms.

A Fixes tag is not required for this change because it is not addressing a
specific bug or issue tracked in a previous commit. Instead, this change is
enhancing the existing functionality to better align with the i.MX6 PCIe
controller’s capabilities.

How about to update the commit as below?
Enable L1SS for the i.MX6 PCIe controller when the `supports_clkreq` flag is
set. This ensures that the PCIe endpoint can enter low-power states
efficiently when the link is not in use.

The commit a00bba406b5a ("PCI: dwc: Advertise L1 PM Substates only if
driver requests it") clears L1SS capabilities by default. However, the
i.MX PCIe controller supports L1SS as indicated by the settings in the L1SS
capabilities register. By setting `dw_pcie.l1ss_support` to true when
`supports_clkreq` is true, enable proper utilization of L1SS for i.MX6 PCIe
configurations.

Best Regards
Richard Zhu