linux-kernel - Re: [PATCH v6 1/4] PCI: dwc: Remove the L1SS check before putting the link into L2

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Message-ID: <20250924194457.GA2131297@bhelgaas>
Date: Wed, 24 Sep 2025 14:44:57 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Richard Zhu <hongxing.zhu@....com>
Cc: frank.li@....com, jingoohan1@...il.com, l.stach@...gutronix.de,
	lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
	robh@...nel.org, bhelgaas@...gle.com, shawnguo@...nel.org,
	s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v6 1/4] PCI: dwc: Remove the L1SS check before putting
 the link into L2

On Wed, Sep 24, 2025 at 03:23:21PM +0800, Richard Zhu wrote:
> The ASPM configuration shouldn't leak out here. Remove the L1SS check
> during L2 entry.

I'm all in favor of removing this code if possible, but we need to
explain why this is safe.  The L1SS check was added for some reason,
and we need to explain why that reason doesn't apply.

> Cc: stable@...r.kernel.org
> Fixes: 4774faf854f5 ("PCI: dwc: Implement generic suspend/resume functionality")
> Suggested-by: Bjorn Helgaas <helgaas@...nel.org>
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 952f8594b501..9d46d1f0334b 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -1005,17 +1005,9 @@ static int dw_pcie_pme_turn_off(struct dw_pcie *pci)
>  
>  int dw_pcie_suspend_noirq(struct dw_pcie *pci)
>  {
> -	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
>  	u32 val;
>  	int ret;
>  
> -	/*
> -	 * If L1SS is supported, then do not put the link into L2 as some
> -	 * devices such as NVMe expect low resume latency.
> -	 */
> -	if (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) & PCI_EXP_LNKCTL_ASPM_L1)
> -		return 0;
> -
>  	if (pci->pp.ops->pme_turn_off) {
>  		pci->pp.ops->pme_turn_off(&pci->pp);
>  	} else {
> -- 
> 2.37.1
>