linux-kernel - Re: [PATCH] rt2x00: BUG: remove double loop on REGISTER_BUSY

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Date:	Fri, 4 Apr 2014 16:17:04 +0200
From:	Richard Genoud <richard.genoud@...il.com>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Jakub Kiciński <moorray3@...pl>,
	Ivo van Doorn <IvDoorn@...il.com>,
	Gertjan van Wingerde <gwingerde@...il.com>,
	Helmut Schaa <helmut.schaa@...glemail.com>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rt2x00: BUG: remove double loop on REGISTER_BUSY_COUNT

2014-04-04 16:06 GMT+02:00 Stanislaw Gruszka <sgruszka@...hat.com>:
> On Fri, Apr 04, 2014 at 11:01:06AM +0200, Jakub Kiciński wrote:
>> On Fri, 4 Apr 2014 10:19:09 +0200, Stanislaw Gruszka wrote:
>> > On Thu, Apr 03, 2014 at 05:37:01PM +0200, Jakub Kiciński wrote:
>> > > On Thu,  3 Apr 2014 16:12:07 +0200, Richard Genoud wrote:
>> > > > rt2x00usb_register_read_lock() calls rt2x00usb_vendor_req_buff_lock()
>> > > > that calls rt2x00usb_vendor_request() which is already looping up to
>> > > > REGISTER_BUSY_COUNT times.
>> > > >
>> > > > So this loop is not needed.
>> > >
>> > > Not true.  rt2x00usb_vendor_request() busy-waits for usb_control_msg()
>> > > to succeed, rt2x00usb_register_read_lock() busy-waits for the register
>> > > field itself to become 0.
>> >
>> > Yeah, but still we are looping REGISTER_BUSY_COUNT*REGISTER_BUSY_COUNT
>> > what seems to be far too long.
>>
>> Yes, the busy waiting itself takes roughly 1s (100*100*100us) and then
>> there are transfer times, so it might be too long indeed.  Vendor driver
>> waits only 10 * 5ms in RTUSB_VendorRequest() so
>
> We use "timeout" argument which is set to 500ms , so perhaps that
> could be the reason why Richard sees "infinite" loop i.e.
> 100*100*(500ms + 100us)
That's what I thougth at the begining, so I applied this patch, but it
was still looping on errors -EPROTO.

>> rt2x00usb_vendor_request() seems like a better place to cut down the
>> number of loops.
>>
>> Alternatively we could make rt2x00usb_regbusy_read() check the retval
>> from rt2x00usb_vendor_request() and exit early?
>
> Make sense, but I think we should review the area and make some more
> changes to fine tune the timeout of USB reg reading functions.
>
> Stanislaw
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