linux-kernel - Re: [PATCH v12 4/8] usb:gadget: Add SuperSpeed support to the Gadget Framework

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Date:	Tue, 24 May 2011 01:14:38 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	Tanya Brokhman <tlinder@...eaurora.org>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, greg@...ah.com,
	linux-usb@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	balbi@...com, ablay@...eaurora.org,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 4/8] usb:gadget: Add SuperSpeed support to the Gadget Framework

On Tue, May 24, 2011 at 01:10, Tanya Brokhman wrote:
>> >+    case USB_REQ_GET_STATUS:
>> >+            if (!gadget_is_superspeed(gadget))
>> >+                    goto unknown;
>> >+            if (ctrl->bRequestType != (USB_DIR_IN | USB_RECIP_INTERFACE))
>> >+                    goto unknown;
>> >+            value = 2;      /* This is the length of the get_status
>> >+            *((__le16 *)req->buf) = 0;
>>
>> Mike please correct me if I'm wrong bug this looks like a case for
>> put_unaligned_le16().
>> Is someone actually using gadget support on blackfin? I'm asking
>> because
>> config_buf() (same file, upstream) is using req->buf to build the
>> descriptors in place and one element is le16 which should be affected.
>
> Mike answered that you're right in your observation. I'm not familiar with
> blackfin. Could you please elaborate on this? I understand that I need to
> use put_unaligned_le16(), will do, but I would like to better understand why
> and if there is a way to test this so that blackfin won't be broken.

not all arches support unaligned accesses.  or they do, but it's done
via (non-trivial) exception processing in software.  req->buf is of
type void* and so presumably is not guaranteed to be aligned on a 2
byte boundary.
-mike
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