Return-path: Received: from 80-190-117-144.ip-home.de ([80.190.117.144]:53806 "EHLO bu3sch.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752164Ab1DFVIs (ORCPT ); Wed, 6 Apr 2011 17:08:48 -0400 Subject: Re: [RFC][PATCH] bcmai: introduce AI driver From: Michael =?ISO-8859-1?Q?B=FCsch?= To: =?UTF-8?Q?Rafa=C5=82_Mi=C5=82ecki?= Cc: Arend van Spriel , "linux-wireless@vger.kernel.org" , "John W. Linville" , Larry Finger , George Kashperko , "b43-dev@lists.infradead.org" , "linux-arm-kernel@lists.infradead.org" , Russell King , Arnd Bergmann , linuxdriverproject , "linux-kernel@vger.kernel.org" In-Reply-To: (sfid-20110406_230206_684163_663F35B6) References: <1302033463-1846-1-git-send-email-zajec5@gmail.com> <1302123428.20093.6.camel@maggie> (sfid-20110406_230206_684163_663F35B6) Content-Type: text/plain; charset="UTF-8" Date: Wed, 06 Apr 2011 23:08:32 +0200 Message-ID: <1302124112.20093.11.camel@maggie> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Wed, 2011-04-06 at 23:01 +0200, Rafał Miłecki wrote: > W dniu 6 kwietnia 2011 22:57 użytkownik Michael Büsch napisał: > > On Wed, 2011-04-06 at 22:42 +0200, Rafał Miłecki wrote: > >> 2011/4/6 Rafał Miłecki : > >> > If we want to have two drivers working on two (different) cores > >> > simultaneously, we will have to add trivial mutex to group core > >> > switching with core operation (read/write). > >> > >> With a little of work we could avoid switching and mutexes on no-host > >> boards. MMIO is not limited to one core at once in such a case. > > > > I don't think that this is a problem at all. > > All that magic does happen inside of the bus I/O handlers. > > Just like SSB does it. > > From a driver point of view, the I/O functions just need to > > be atomic. > > > > For SSB it's not always 100% atomic, but we're always safe > > due to some assumptions being made. But this is an SSB implementation > > detail that is different from AXI. So don't look too closely > > at the SSB implementation of the I/O functions. You certainly want > > to implement them slightly differently in AXI. SSB currently doesn't > > make use of the additional sliding windows, because they are not > > available in the majority of SSB devices. > > > > The AXI bus subsystem will manage the sliding windows and the driver > > doesn't know about the details. > > Sure, I've meant mutex inside bcmai (or whatever name), not on the driver side! > > In BCMAI: > bcmai_read() { > mutex_get(); > switch_core(); > ioread(); > mutex_release(); > } Yeah that basically is the idea. But it's a little bit harder than that. The problem is that the mutex cannot be taken in interrupt context. A spinlock probably is a bit hairy, too, depending on how heavy a core switch is on AXI. On SSB we workaround this with some (dirty but working) assumptions. On AXI you probably can do lockless I/O, if you use the two windows (how many windows are there?) in a clever way to avoid core switching completely after the system was initialized. -- Greetings Michael.