linux-kernel - Re: [PATCH v6 3/4] usb: ehci: Add new EHCI driver for Broadcom STB SoC's

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Date:   Thu, 7 May 2020 08:41:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Alan Cooper <alcooperx@...il.com>,
        ": Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        DTML <devicetree@...r.kernel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        USB list <linux-usb@...r.kernel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v6 3/4] usb: ehci: Add new EHCI driver for Broadcom STB
 SoC's

On Thu, May 07, 2020 at 12:01:16AM +0300, Andy Shevchenko wrote:
> On Wed, May 6, 2020 at 11:23 PM Alan Cooper <alcooperx@...il.com> wrote:
> > On Tue, May 5, 2020 at 7:00 AM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > > On Thu, Apr 30, 2020 at 07:12:57AM -0400, Al Cooper wrote:
> 
> ...
> 
> > > > +     /* Hook the hub control routine to work around a bug */
> > >
> > > What bug?  This feels wrong.
> >
> > The bug is explained in a comment above the ehci_brcm_hub_control()
> > routine as follows:
> > /*
> >  * ehci_brcm_hub_control
> >  * Intercept echi-hcd request to complete RESUME and align it to the start
> >  * of the next microframe.
> >  * If RESUME is complete too late in the microframe, host controller
> >  * detects babble on suspended port and resets the port afterwards.
> >  * This s/w workaround allows to avoid this problem.
> >  * See SWLINUX-1909 for more details
> >  */
> > I'll remove the internal bug tracking reference from the comment.
> 
> I guess you may leave the internal bug reference. I can tell from my
> experience that's hard to understand what was going on in the driver
> in years perspective. It will help whoever in this company have a
> chance to look after the driver.

"internal bug references" mean nothing to the 99% of the people that can
see this.  Document the heck out of what this is instead please.

greg k-h