linux-kernel - Re: [PATCH v2 2/2] USB: hcd-pci: Fully suspend across freeze/thaw cycle

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Date:   Tue, 19 Apr 2022 10:43:02 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Evan Green <evgreen@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Rajat Jain <rajatja@...omium.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Youngjin Jang <yj84.jang@...sung.com>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 2/2] USB: hcd-pci: Fully suspend across freeze/thaw
 cycle

On Mon, Apr 18, 2022 at 02:00:46PM -0700, Evan Green wrote:
> The documentation for the freeze() method says that it "should quiesce
> the device so that it doesn't generate IRQs or DMA". The unspoken
> consequence of not doing this is that MSIs aimed at non-boot CPUs may
> get fully lost if they're sent during the period where the target CPU is
> offline.
> 
> The current callbacks for USB HCD do not fully quiesce interrupts,
> specifically on XHCI. Change to use the full suspend/resume flow for
> freeze/thaw to ensure interrupts are fully quiesced. This fixes issues
> where USB devices fail to thaw during hibernation because XHCI misses
> its interrupt and cannot recover.
> 
> Signed-off-by: Evan Green <evgreen@...omium.org>
> 
> ---

Acked-by: Alan Stern <stern@...land.harvard.edu>

> Changes in v2:
>  - Added the patch modifying the remote wakeup state

That wasn't a change to this patch.  No matter.

>  - Removed the change to freeze_noirq/thaw_noirq
> 
>  drivers/usb/core/hcd-pci.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/core/hcd-pci.c b/drivers/usb/core/hcd-pci.c
> index 8176bc81a635d6..ae5e6d572376be 100644
> --- a/drivers/usb/core/hcd-pci.c
> +++ b/drivers/usb/core/hcd-pci.c
> @@ -616,10 +616,10 @@ const struct dev_pm_ops usb_hcd_pci_pm_ops = {
>  	.suspend_noirq	= hcd_pci_suspend_noirq,
>  	.resume_noirq	= hcd_pci_resume_noirq,
>  	.resume		= hcd_pci_resume,
> -	.freeze		= check_root_hub_suspended,
> +	.freeze		= hcd_pci_suspend,
>  	.freeze_noirq	= check_root_hub_suspended,
>  	.thaw_noirq	= NULL,
> -	.thaw		= NULL,
> +	.thaw		= hcd_pci_resume,
>  	.poweroff	= hcd_pci_suspend,
>  	.poweroff_noirq	= hcd_pci_suspend_noirq,
>  	.restore_noirq	= hcd_pci_resume_noirq,