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

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Date:	Fri, 4 Apr 2014 11:01:06 +0200
From:	Jakub Kiciński <moorray3@...pl>
To:	Stanislaw Gruszka <sgruszka@...hat.com>
Cc:	Richard Genoud <richard.genoud@...il.com>,
	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
Subject: Re: [PATCH] rt2x00: BUG: remove double loop on REGISTER_BUSY_COUNT

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
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?

	-- kuba

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