linux-kernel - Re: [PATCH] xhci: Don't use soft retry if slot id

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Date:   Mon, 14 Oct 2019 11:06:40 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Bernhard Gebetsberger <bernhard.gebetsberger@....at>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xhci: Don't use soft retry if slot id > 0

On 13.10.2019 3.33, Bernhard Gebetsberger wrote:
> According to the xhci specification(chapter 4.6.8.1) soft retry
> shouldn't be used if the slot id is higher than 0. Currently some usb
> devices break on some systems because soft retry is being used when
> there is a transaction error, without checking the slot id.
> 
That is not correct

Specs say that soft retry should not be used if we are dealing with a
FS/LS device behind a HS hub, this can be checked from the "TT Hub Slot ID"
field in the slot context, which we do.

In xhci all devices have a slot id, so this change would prevent
soft retry almost completely.

Specs 4.6.8.1:
"Soft Retry attempts shall not be performed if the device is behind a
TT in a HS Hub (i.e. TT Hub Slot ID > ‘0’)."

-Mathias