Return-path: Received: from mail.academy.zt.ua ([82.207.120.245]:14583 "EHLO mail.academy.zt.ua" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751191Ab1DFVVU (ORCPT ); Wed, 6 Apr 2011 17:21:20 -0400 Subject: Re: [RFC][PATCH] bcmai: introduce AI driver From: George Kashperko 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: References: <1302033463-1846-1-git-send-email-zajec5@gmail.com> <1302123428.20093.6.camel@maggie> <1302124112.20093.11.camel@maggie> Content-Type: text/plain; charset=UTF-8 Date: Thu, 07 Apr 2011 00:18:57 +0300 Message-Id: <1302124737.27258.7.camel@dev.znau.edu.ua> Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: > W dniu 6 kwietnia 2011 23:08 użytkownik Michael Büsch napisał: > > 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. > > We have 2 windows. I didn't try this, but let's assume they have no > limitations. We can use first window for one driver only, second > driver for second driver only. That gives us 2 drivers simultaneously > working drivers. No driver need to reset core really often (and not > inside interrupt context) so we will switch driver's window to agent > (from core) only at init/reset. > > The question is what amount of driver we will need to support at the same time. > I guess (correct me please, Broadcom guys if I'm wrong) there are two functions two-head w11 pci host and therefore 4 sliding windows, 2 per each function. You really was in need for core switching for PCI SSB hosts, but seem all that stuff for PCI switching in current bcm80211/utils code is rudimentary stuff left from PCI times when you was required to use sliding window for chipcommon and pci bridge core access. Have nice day, George