Date:   Wed, 29 Dec 2021 10:51:23 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Puma Hsu <pumahsu@google.com>
Cc:     mathias.nyman@intel.com, Albert Wang <albertccwang@google.com>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] xhci: re-initialize the HC during resume if HCE was set
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On Wed, Dec 29, 2021 at 05:11:47PM +0800, Puma Hsu wrote:
> On Wed, Dec 29, 2021 at 4:30 PM Greg KH <gregkh@linuxfoundation.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.

Given that your product platform is an older kernel version than 5.17, I
think that you also want this in the older kernel releases, so please
mark it for stable backporting.

thanks,

greg k-h