linux-kernel - Re: [PATCH] xhci: re-initialize the HC during resume if HCE was set

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Date:   Wed, 29 Dec 2021 17:11:47 +0800
From:   Puma Hsu <pumahsu@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     mathias.nyman@...el.com, Albert Wang <albertccwang@...gle.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xhci: re-initialize the HC during resume if HCE was set

On Wed, Dec 29, 2021 at 4:30 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> A: http://en.wikipedia.org/wiki/Top_post
> Q: Were do I find info about this thing called top-posting?
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
> A: No.
> Q: Should I include quotations after my reply?
>
> http://daringfireball.net/2007/07/on_top
>
> On Wed, Dec 29, 2021 at 01:53:04PM +0800, Puma Hsu wrote:
> > This commit is not used to fix a specific commit. We find a condition
> > that when XHCI runs the resume process but the HCE flag is set, then
> > the Run/Stop bit of USBCMD cannot be set so that HC would not be
> > enabled. In fact, HC may already meet a problem at this moment.
> > Besides, in xHCI requirements specification revision 1.2, Table 5-21
> > BIT(12) claims that Software should re-initialize the xHC when HCE is
> > set. Therefore, I think this commit could be the error handling for
> > HCE.
>
> So this does not actually fix an issue that you have seen in any device
> or testing?  So it is not relevant for older kernels but just "nice to
> have"?
>
> How did you test this if you can not duplicate the problem?
>

Yes, we actually see that the HCE may be detected while running xhci_resume
on our product platform, so I'm able to verify this commit can fix
such a condition.
For older kernels, I'm not sure whether someone had ever met such issue, but I
believe the Run/Stop bit of USBCMD cannot be set once HCE is raised.

Thanks.
Puma Hsu

> thanks,
>
> greg k-h