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Subject: Re: [PATCH] xhci: workaround CSS timeout on AMD SNPS 3.0 xHC.
From:   Kai Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <1542356426-10299-1-git-send-email-Sandeep.Singh@amd.com>
Date:   Fri, 16 Nov 2018 16:35:47 +0800
Cc:     "mathias.nyman@intel.com" <mathias.nyman@intel.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "S-k, Shyam-sundar" <Shyam-sundar.S-k@amd.com>,
        "Shah, Nehal-bakulchandra" <Nehal-bakulchandra.Shah@amd.com>
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Message-Id: <0B58593B-1CE2-49EB-9F13-A2BC449AB8E8@canonical.com>
References: <1542356426-10299-1-git-send-email-Sandeep.Singh@amd.com>
To:     "Singh, Sandeep" <Sandeep.Singh@amd.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Sandeep,

> On Nov 16, 2018, at 16:21, Singh, Sandeep <Sandeep.Singh@amd.com> wrote:
> 
> From: Sandeep Singh <sandeep.singh@amd.com>
> 
> Occasionally AMD SNPS 3.0 xHC does not respond to
> CSS when set, also it does not flag anything on SRE and HCE
> to point the internal xHC errors on USBSTS register. This stalls
> the entire system wide suspend and there is no point in stalling
> just because of xHC CSS is not responding.
> 
> To work around this problem, if the xHC does not flag
> anything on SRE and HCE, we can skip the CSS
> timeout and allow the system to continue the suspend. Once the
> system resume happens we can internally reset the controller
> using XHCI_RESET_ON_RESUME quirk.

What happens to the connected and suspended USB devices?
Do USB devices lose remote wakeup functionality when this happens?

> 
> Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
> Signed-off-by: Sandeep Singh <Sandeep.Singh@amd.com>
> cc: Nehal Shah <Nehal-bakulchandra.Shah@amd.com>
> ---
> drivers/usb/host/xhci-pci.c |  4 ++++
> drivers/usb/host/xhci.c     | 25 +++++++++++++++++++++++++
> drivers/usb/host/xhci.h     |  1 +
> 3 files changed, 30 insertions(+)
> 
> diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
> index 01c5705..72493c4 100644
> --- a/drivers/usb/host/xhci-pci.c
> +++ b/drivers/usb/host/xhci-pci.c
> @@ -139,6 +139,10 @@ static void xhci_pci_quirks(struct device *dev, struct xhci_hcd *xhci)
> 		 pdev->device == 0x43bb))
> 		xhci->quirks |= XHCI_SUSPEND_DELAY;
> 
> +	if (pdev->vendor == PCI_VENDOR_ID_AMD &&
> +	    (pdev->device == 0x15e0 || pdev->device == 0x15e1))
> +		xhci->quirks |= XHCI_SNPS_BROKEN_SUSPEND;
> +
> 	if (pdev->vendor == PCI_VENDOR_ID_AMD)
> 		xhci->quirks |= XHCI_TRUST_TX_LENGTH;
> 
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index 0420eef..965b503 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -970,6 +970,7 @@ int xhci_suspend(struct xhci_hcd *xhci, bool do_wakeup)
> 	unsigned int		delay = XHCI_MAX_HALT_USEC;
> 	struct usb_hcd		*hcd = xhci_to_hcd(xhci);
> 	u32			command;
> +	u32			res;
> 
> 	if (!hcd->state)
> 		return 0;
> @@ -1025,10 +1026,32 @@ int xhci_suspend(struct xhci_hcd *xhci, bool do_wakeup)
> 	writel(command, &xhci->op_regs->command);
> 	if (xhci_handshake(&xhci->op_regs->status,
> 				STS_SAVE, 0, 10 * 1000)) {
> +		if (xhci->quirks & XHCI_SNPS_BROKEN_SUSPEND) {
> +		       /*
> +			* AMD SNPS xHC 3.0 occasionally does not clear the
> +			* SSS bit of USBSTS and when driver tries to poll
> +			* to see if the xHC clears BIT(8) which never happens
> +			* and driver assumes that controller is not responding
> +			* and times out. To workaround this, its good to check
> +			* if SRE and HCE bits are not set (as per xhci
> +			* Section 5.4.2) and bypass the timeout.
> +			*/
> +
> +			res = readl(&xhci->op_regs->status);
> +			if (res & STS_SAVE) {
> +				if (((res & STS_SRE) == 0) &&
> +				    ((res & STS_HCE) == 0)) {
> +					xhci->quirks |= XHCI_RESET_ON_RESUME;
> +					goto complete_suspend;
> +				}
> +			}

Maybe merge the two “ifs”? There are no other conditions to handle.

Kai-Heng

> +		}
> +
> 		xhci_warn(xhci, "WARN: xHC save state timeout\n");
> 		spin_unlock_irq(&xhci->lock);
> 		return -ETIMEDOUT;
> 	}
> + complete_suspend:
> 	spin_unlock_irq(&xhci->lock);
> 
> 	/*
> @@ -1213,6 +1236,8 @@ int xhci_resume(struct xhci_hcd *xhci, bool hibernated)
> 	usb_hcd_poll_rh_status(xhci->shared_hcd);
> 	set_bit(HCD_FLAG_POLL_RH, &hcd->flags);
> 	usb_hcd_poll_rh_status(hcd);
> +	if (xhci->quirks & XHCI_SNPS_BROKEN_SUSPEND)
> +		xhci->quirks &= ~XHCI_RESET_ON_RESUME;
> 
> 	return retval;
> }
> diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
> index bf0b369..eb99782 100644
> --- a/drivers/usb/host/xhci.h
> +++ b/drivers/usb/host/xhci.h
> @@ -1849,6 +1849,7 @@ struct xhci_hcd {
> #define XHCI_INTEL_USB_ROLE_SW	BIT_ULL(31)
> #define XHCI_ZERO_64B_REGS	BIT_ULL(32)
> #define XHCI_DEFAULT_PM_RUNTIME_ALLOW	BIT_ULL(33)
> +#define XHCI_SNPS_BROKEN_SUSPEND	BIT_ULL(34)
> 
> 	unsigned int		num_active_eps;
> 	unsigned int		limit_active_eps;
> -- 
> 2.7.4
>