Return-path: Received: from kroah.org ([198.145.64.141]:57401 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751011Ab1DSODC (ORCPT ); Tue, 19 Apr 2011 10:03:02 -0400 Date: Tue, 19 Apr 2011 07:02:57 -0700 From: Greg KH To: Arend van Spriel Cc: =?utf-8?B?UmFmYcWCIE1pxYJlY2tp?= , Arnd Bergmann , George Kashperko , Hauke Mehrtens , Russell King , "linux-kernel@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Jonas Gorski , "b43-dev@lists.infradead.org" , Andy Botting , Larry Finger Subject: Re: Could I (ab)use bus (struct bus_type) for virtual Broadcom bus? Message-ID: <20110419140257.GA20456@kroah.com> References: <1302892585.30441.12.camel@dev.znau.edu.ua> <201104171938.12834.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: Sender: linux-wireless-owner@vger.kernel.org List-ID: On Tue, Apr 19, 2011 at 03:58:32PM +0200, Arend van Spriel wrote: > On Sun, 17 Apr 2011 19:38:12 +0200, Arnd Bergmann wrote: > > Hi Rafał, > > As you probably expected I tried to integrate and use your bcmai/bcmaxi/? > driver with our brcm80211 driver (making progress). In the mean time > I tried to follow the discussions going on, but I am still catching > up. > > >Compare this to the PCI bus type, which essentially deals with devices > >that have a PCI configuration space that contains generic (irq, memory, > >vendor/device ID, ...) registers along with device specific registers. > > How much alike is the (BCM)AXI bus type? My assumption was that each > registered PCI device is handled by a single driver module. In the > current(?) bcmai implementation each device driver is called with the > appropriate device structure reference, but it will also have the bus > structure reference and through that can also access other cores on the > (bcm)axi bus. This seems to me a potential issue when there are no > synchronization mechanisms in place (whether in a SoC configuration or > PCI-hosted). Does the PCI bus type allow driver for device A access > device B? > > >A new bus_type really only makes sense if you expect a lot of devices > >to use this and you want to have the probing in the bus. If you only > >want to have a way to enumerate devices that get created by the > >parent driver, you can also use platform devices. > > The main assumption of the (bcm)axi driver seems to be that each core can > be considered as a device. Correct me if I am wrong, but I consider a > device to be an entity providing a particular system function. So an > ethernet device provides ethernet connectivity function, a mixer device > provides sound mixing function, and so on. The cores within a chip are not > always self-contained like this. To clarify let's say a system function is > realized by programming core A, core B, and finally trigger core A to set > the function in motion. This implies the need of coordination between the > programming steps on those cores. > > Is my view on what is a device wrong? Does a platform device differ in > this respect from a regular device? Please don't use a platform device, unless there is no other way for your device to work. For this device, you are connected to the PCI bus, so a platform device does not make sense at all. thanks, greg k-h