Re: [PATCH v2 04/12] PCI: qcom: Add support for disabling ASPM L0s in devicetree

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Feb 23, 2024 at 04:21:16PM +0100, Johan Hovold wrote:
> Commit 9f4f3dfad8cf ("PCI: qcom: Enable ASPM for platforms supporting
> 1.9.0 ops") started enabling ASPM unconditionally when the hardware
> claims to support it. This triggers Correctable Errors for some PCIe
> devices on machines like the Lenovo ThinkPad X13s, which could indicate
> an incomplete driver ASPM implementation or that the hardware does in
> fact not support L0s.

Are there any more details about this?  Do the errors occur around
suspend/resume, a power state transition, or some other event?  Might
other DWC-based devices be susceptible?  Is there a specific driver
you suspect might be incomplete?

Do you want the DT approach because the problem is believed to be
platform-specific?  Otherwise, maybe we should consider reverting
9f4f3dfad8cf until the problem is understood?

Could this be done via a quirk like quirk_disable_aspm_l0s()?  That
currently uses pci_disable_link_state(), which I don't think is
completely safe because it leaves the possibility that drivers or
users could re-enable L0s, e.g., via sysfs.

This patch is nice because IIUC it directly changes PCI_EXP_LNKCAP,
which avoids that issue, but quirk_disable_aspm_l0s() could
conceivably be reimplemented to cache PCI_EXP_LNKCAP in struct pci_dev
so quirks could override it, as we do with struct pci_dev.devcap.

> Add support for disabling ASPM L0s in the devicetree when it is not
> supported on a particular machine and controller.
> 
> Note that only the 1.9.0 ops enable ASPM currently.
> 
> Fixes: 9f4f3dfad8cf ("PCI: qcom: Enable ASPM for platforms supporting 1.9.0 ops")
> Cc: stable@vger.kernel.org      # 6.7
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 09d485df34b9..0fb5dc06d2ef 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -273,6 +273,25 @@ static int qcom_pcie_start_link(struct dw_pcie *pci)
>  	return 0;
>  }
>  
> +static void qcom_pcie_clear_aspm_l0s(struct dw_pcie *pci)
> +{
> +	u16 offset;
> +	u32 val;
> +
> +	if (!of_property_read_bool(pci->dev->of_node, "aspm-no-l0s"))
> +		return;
> +
> +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +
> +	dw_pcie_dbi_ro_wr_en(pci);
> +
> +	val = readl(pci->dbi_base + offset + PCI_EXP_LNKCAP);
> +	val &= ~PCI_EXP_LNKCAP_ASPM_L0S;
> +	writel(val, pci->dbi_base + offset + PCI_EXP_LNKCAP);
> +
> +	dw_pcie_dbi_ro_wr_dis(pci);
> +}
> +
>  static void qcom_pcie_clear_hpc(struct dw_pcie *pci)
>  {
>  	u16 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> @@ -962,6 +981,7 @@ static int qcom_pcie_init_2_7_0(struct qcom_pcie *pcie)
>  
>  static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
>  {
> +	qcom_pcie_clear_aspm_l0s(pcie->pci);
>  	qcom_pcie_clear_hpc(pcie->pci);
>  
>  	return 0;
> -- 
> 2.43.0
>