linux-kernel - Re: [PATCH v3] PCI: dwc: Clean up some unnecessary codes in dw_pcie_suspend

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Message-ID: <ZzzUa8Zs3qJiVPam@lizhi-Precision-Tower-5810>
Date: Tue, 19 Nov 2024 13:09:47 -0500
From: Frank Li <Frank.li@....com>
To: Richard Zhu <hongxing.zhu@....com>
Cc: jingoohan1@...il.com, bhelgaas@...gle.com, lpieralisi@...nel.org,
	kw@...ux.com, manivannan.sadhasivam@...aro.org, robh@...nel.org,
	imx@...ts.linux.dev, kernel@...gutronix.de,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PCI: dwc: Clean up some unnecessary codes in
 dw_pcie_suspend_noirq()

On Mon, Nov 18, 2024 at 01:44:47PM +0800, Richard Zhu wrote:
> Before sending PME_TURN_OFF, don't test the LTSSM state. Since it's safe
> to send PME_TURN_OFF message regardless of whether the link is up or
> down. So, there would be no need to test the LTSSM state before sending
> PME_TURN_OFF message.
>
> Only print the message when ltssm_stat is not in DETECT and POLL.
> In the other words, there isn't an error message when no endpoint is
> connected at all.
>
> Also, when the endpoint is connected and PME_TURN_OFF is sent, do not return
> error if the link doesn't enter L2. Just print a warning and continue with the
> suspend as the link will be recovered in dw_pcie_resume_noirq().
>
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> ---
> v3 changes:
> - Refine the commit message refer to Manivannan's comments.
> - Regarding Frank's comments, avoid 10ms wait when no link up.
> v2 changes:
> - Don't remove L2 poll check.
> - Add one 1us delay after L2 entry.
> - No error return when L2 entry is timeout
> - Don't print message when no link up.
> ---
>  .../pci/controller/dwc/pcie-designware-host.c | 40 ++++++++++---------
>  drivers/pci/controller/dwc/pcie-designware.h  |  1 +
>  2 files changed, 23 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 24e89b66b772..68fbc16199e8 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -927,24 +927,28 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
>  	if (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) & PCI_EXP_LNKCTL_ASPM_L1)
>  		return 0;
>
> -	/* Only send out PME_TURN_OFF when PCIE link is up */
> -	if (dw_pcie_get_ltssm(pci) > DW_PCIE_LTSSM_DETECT_ACT) {
> -		if (pci->pp.ops->pme_turn_off)
> -			pci->pp.ops->pme_turn_off(&pci->pp);
> -		else
> -			ret = dw_pcie_pme_turn_off(pci);
> -
> -		if (ret)
> -			return ret;
> +	if (pci->pp.ops->pme_turn_off)
> +		pci->pp.ops->pme_turn_off(&pci->pp);
> +	else
> +		ret = dw_pcie_pme_turn_off(pci);
> +	if (ret)
> +		return ret;
>
> -		ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
> -					PCIE_PME_TO_L2_TIMEOUT_US/10,
> -					PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
> -		if (ret) {
> -			dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
> -			return ret;
> -		}
> -	}
> +	ret = read_poll_timeout(dw_pcie_get_ltssm, val,
> +				val == DW_PCIE_LTSSM_L2_IDLE ||
> +				val <= DW_PCIE_LTSSM_DETECT_WAIT,
> +				PCIE_PME_TO_L2_TIMEOUT_US/10,
> +				PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
> +	if (ret && (val > DW_PCIE_LTSSM_DETECT_WAIT))

if true of (val <= DW_PCIE_LTSSM_DETECT_WAIT), which means not device
attached, 'ret' should be 0.

when ret is not 0, means, link up and not in L2 idle status. So check
'(val > DW_PCIE_LTSSM_DETECT_WAIT)' is redundant.

NOT(val == DW_PCIE_LTSSM_L2_IDLE || val <= DW_PCIE_LTSSM_DETECT_WAIT)
equal
(val != DW_PCIE_LTSSM_L2_IDLE) && (val > DW_PCIE_LTSSM_DETECT_WAIT)

Frank

> +		/* Only dump message when ltssm_stat isn't in DETECT and POLL */
> +		dev_warn(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
> +	else
> +		/*
> +		 * Refer to r6.0, sec 5.3.3.2.1, software should wait at least
> +		 * 100ns after L2/L3 Ready before turning off refclock and
> +		 * main power. It's harmless too when no endpoint connected.
> +		 */
> +		udelay(1);
>
>  	dw_pcie_stop_link(pci);
>  	if (pci->pp.ops->deinit)
> @@ -952,7 +956,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
>
>  	pci->suspended = true;
>
> -	return ret;
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(dw_pcie_suspend_noirq);
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 347ab74ac35a..bf036e66717e 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -330,6 +330,7 @@ enum dw_pcie_ltssm {
>  	/* Need to align with PCIE_PORT_DEBUG0 bits 0:5 */
>  	DW_PCIE_LTSSM_DETECT_QUIET = 0x0,
>  	DW_PCIE_LTSSM_DETECT_ACT = 0x1,
> +	DW_PCIE_LTSSM_DETECT_WAIT = 0x6,
>  	DW_PCIE_LTSSM_L0 = 0x11,
>  	DW_PCIE_LTSSM_L2_IDLE = 0x15,
>
> --
> 2.37.1
>