Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751675AbWBWJd5 (ORCPT ); Thu, 23 Feb 2006 04:33:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751674AbWBWJd5 (ORCPT ); Thu, 23 Feb 2006 04:33:57 -0500 Received: from caramon.arm.linux.org.uk ([212.18.232.186]:7440 "EHLO caramon.arm.linux.org.uk") by vger.kernel.org with ESMTP id S1751082AbWBWJd4 (ORCPT ); Thu, 23 Feb 2006 04:33:56 -0500 Date: Thu, 23 Feb 2006 09:33:48 +0000 From: Russell King To: Kumar Gala Cc: Greg KH , linux-kernel@vger.kernel.org Subject: Re: what's a platform device? Message-ID: <20060223093348.GB6248@flint.arm.linux.org.uk> Mail-Followup-To: Kumar Gala , Greg KH , linux-kernel@vger.kernel.org References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1966 Lines: 41 On Wed, Feb 22, 2006 at 03:47:40PM -0600, Kumar Gala wrote: > The situation I have is an FPGA connected over PCI. The FPGA implements > various device functionality (serial ports, I2C controller, IR, etc.) as a > single PCI device/function. The FPGA breaks any notion of a true PCI > device, it uses PCI as a device interconnect more than anything else. We have at least one example where we have a single PCI function containing more than one type of functionality which are the parallel port and serial cards [*]. Normally, the different types of functionality are accessible via different BARs which at least gives some logical separation. It's not really a good model because you have to have a special PCI probe driver to register the various functionalities with the subsystems rather than using the generic 8250_pci and parport_pci drivers directly. Also it can have problems if you want to have (eg) serial built-in and i2c as a module. The alternative as Greg points out is to implement a pseudo bus_type, but I start to worry about the overhead associated with doing so. Given the choice between a small PCI "probe" driver for a small number of functionalities and a complete driver model infrastructure, I'd prefer the former over the latter. * - I'm slightly biased here because it seems I've ended up "owning" the serial parts of parport_serial, though I don't want to admit that in public. (damn, I just did!) I think that, provided the subsystems are sanely written such that there is very little or no code duplication, this method is as good as any other method. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: 2.6 Serial core - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/