linux-kernel - Re: [PATCH v2] usb: misc: ehset: Workaround for "special" hubs

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Date:   Thu, 7 Oct 2021 12:47:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     Razvan Heghedus <heghedus.razvan@...il.com>,
        Peter Chen <peter.chen@....com>,
        Anant Thazhemadam <anant.thazhemadam@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: misc: ehset: Workaround for "special" hubs

On Thu, Oct 07, 2021 at 12:21:12PM +0200, Johan Hovold wrote:
> On Wed, Sep 15, 2021 at 03:16:13PM +0300, Razvan Heghedus wrote:
> > The USB2.0 spec chapter 11.24.2.13 says that the USB port which is going
> > under test needs to be put in suspend state before sending the test
> > command. Many hubs, don't enforce this precondition and they work fine
> > without this step. But there are some "special" hubs, which requires to
> > disable the port power before sending the test command.
> 
> So you're essentially doing two things in one patch here; you now
> sending a suspend request for all hubs except a for the ones in the
> quirk list that are sent a port power disable.
> 
> This isn't really reflected in the commit summary which says "workaround
> for special hubs" as you're also changing the default implementation.
> 
> Probably better handled in two patches, or at least this needs to be
> reflected in the commit summary/message better.
> 
> But this patch is so broken that I just sent a revert. There also some
> style issues that should be addressed if you send a new version.
> 
> > Because the USB spec mention that the port should be suspended, also
> > do this step before sending the test command. This could rise the
> > problem with other hubs which are not compliant with the spec and the
> > test command will not work if the port is suspend. If such hubs are
> > found, a similar workaround like the disable part could be implemented
> > to skip the suspend port command.
> > 
> > Signed-off-by: Razvan Heghedus <heghedus.razvan@...il.com>
> > ---
> >  Changes in v2:
> >   - style change regarding multi-line comments and a new black line
> >     after local variable definitions
> >   - No more corporate email annotation
> > This time without that corporate email annotation.
> > Also has a couple of style changes regardind multi-line comments and a
> > black line after local variable definitions.
> >
> >  drivers/usb/misc/ehset.c | 81 ++++++++++++++++++++++++++++++++--------
> >  1 file changed, 65 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/usb/misc/ehset.c b/drivers/usb/misc/ehset.c
> > index f87890f9cd26..b848bbdee802 100644
> > --- a/drivers/usb/misc/ehset.c
> > +++ b/drivers/usb/misc/ehset.c
> > @@ -18,6 +18,47 @@
> >  #define TEST_SINGLE_STEP_GET_DEV_DESC		0x0107
> >  #define TEST_SINGLE_STEP_SET_FEATURE		0x0108
> >  
> > +/*
> > + * A list of USB hubs which requires to disable the power
> > + * to the port before starting the testing procedures.
> > + */
> > +static const struct usb_device_id ehset_hub_list[] = {
> > +	{USB_DEVICE(0x0424, 0x4502)},
> > +	{USB_DEVICE(0x0424, 0x4913)},
> > +	{USB_DEVICE(0x0451, 0x8027)},
> > +	{}
> 
> Missing spaces after { and before }.
> 
> > +};
> > +
> > +static int ehset_prepare_port_for_testing(struct usb_device *hub_udev, u16 portnum)
> > +{
> > +	int ret = 0;
> > +
> > +	/*
> > +	 * The USB2.0 spec chapter 11.24.2.13 says that the USB port which is
> > +	 * going under test needs to be put in suspend before sending the
> > +	 * test command. Most hubs don't enforce this precondition, but there
> > +	 * are some hubs which needs to disable the power to the port before
> > +	 * starting the test.
> > +	 */
> > +	if (usb_match_id(to_usb_interface(hub_udev->dev.parent), ehset_hub_list)) {
> 
> This is the main problem: hub_udev->dev.parent does not represent a USB
> interface so you cannot use to_usb_interface() or you'd pass a random
> pointer to usb_match_id().
> 
> If hub_udev is a root hub, then hub_udev->dev.parent does not even
> represent a USB device (but, for example, the parent PCI device).

Ugh, good catch, I totally missed this.

I'll go apply the revert now, thank you so much for it.

Razvan, how did you test this?

thanks,

greg k-h