linux-kernel - Re: [PATCH] usb-core: Add MS_INTR

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Date:   Sun, 12 Mar 2017 22:47:13 +0100
From:   Samuel Thibault <samuel.thibault@...-lyon.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, dave@...lke.cc,
        kevin.derome@...tech.eu, clause.andreabush@...il.com,
        mengualjeanphi@...e.fr
Subject: Re: [PATCH] usb-core: Add MS_INTR_BINTERVAL USB quirk

Alan Stern, on dim. 12 mars 2017 17:18:51 -0400, wrote:
> Interesting.  This is a high-speed device that mistakenly uses the 
> low/full-speed encoding for an interrupt bInterval value?

Yes...

> That's pretty unusual.  Most HID devices (which includes the Braille
> devices I have heard of) run at low speed, and a few of them run at 
> full speed.  I can't remember any running at high speed.

That's the first device for which we have such issue.  We'll try to
check whether some other devices need the same quirk.

> > +			 */
> > +			/*
> > +			 * This quirk fixes bIntervals reported in ms.
> > +			 */
> > +			if (to_usb_device(ddev)->quirks &
> > +				USB_QUIRK_MS_INTR_BINTERVAL)
> > +				i = j = n;
> 
> You want to use the bInterval value the device intended to provide, not
> a default value.

n is alreay computed as such above, but OK :) (and better clamp anyway)

> > +	/* Baum Vario Ultra */
> > +	{ USB_DEVICE(0x0904, 0x6101), .driver_info =
> > +			USB_QUIRK_MS_INTR_BINTERVAL },
> > +	{ USB_DEVICE(0x0904, 0x6102), .driver_info =
> > +			USB_QUIRK_MS_INTR_BINTERVAL },
> > +	{ USB_DEVICE(0x0904, 0x6103), .driver_info =
> > +			USB_QUIRK_MS_INTR_BINTERVAL },
> 
> You didn't read the comment at the start of the file.  :-)  This list
> is supposed to remain sorted by vendor and product ID.

D'oh, sorry :)

Samuel