From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from canuck.infradead.org (canuck.infradead.org [209.217.80.40]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 928FFDDECB for ; Fri, 8 Jun 2007 02:06:56 +1000 (EST) Subject: Re: [PATCH] powerpc: Create "rom" (MTD) device prpmc2800 From: David Woodhouse To: Segher Boessenkool In-Reply-To: <18fbfbaf113ab76b602d279848d9b405@kernel.crashing.org> References: <7fc919fce0761f861be3069a853d3169@bga.com> <4662EAA9.70104@ru.mvista.com> <466308F4.8050004@ru.mvista.com> <8ac5664208e0f59329b62ac2138bbc8c@kernel.crashing.org> <466312C2.4090200@ru.mvista.com> <548a7e11ffb577f6395b8f5a9c2fba2d@kernel.crashing.org> <466323EF.5040807@ru.mvista.com> <1181228442.2785.60.camel@pmac.infradead.org> <18fbfbaf113ab76b602d279848d9b405@kernel.crashing.org> Content-Type: text/plain Date: Thu, 07 Jun 2007 17:05:58 +0100 Message-Id: <1181232358.2785.79.camel@pmac.infradead.org> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, linux-mtd@lists.infradead.org, Milton Miller List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2007-06-07 at 17:55 +0200, Segher Boessenkool wrote: > > Any representation of flash devices in the device-tree should ideally > > have 'bus width' and 'interleave' properties to contain this > > information. > > > > The 'bus width' cannot necessarily be inferred, especially where a > > given > > bus can be configured to allow multiple sizes of access. It's purely a > > function of how the flash chips are wired up. That's why we actually > > call it 'bank width', not 'bus width' in the Linux code. > > Ah, "bank width" as in "bus width" per chip select. I see. > > So I think the best thing to have would be > > compatible "cfi-flash" > bank-width like you said > device-width width of a single flash device > reg complete address range of this thing > > and then the Linux OF CFI flash code / MTD code just keeps > on probing devices from that address range until it has it > filled. > > Sounds good / comments / anything I missed? That seems reasonable. I would personally have used 'interleave' to give the number of devices interleaved together into the specified bank-width, rather than specifying device-width. People might get confused by device-width because many devices can actually be _either_ x16 or x8. But I don't care much. Linux will only be using the bank-width anyway. The other thing that might be seen in the 'compatible' property would be 'jedec-flash', and in that case perhaps we also want properties for the manufacturer and device ident? Linux wouldn't necessarily care about them, but other operating systems might. And we also need partition information to get through somehow, in the cases where the firmware knows it. -- dwmw2