From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 8 Feb 2008 17:14:51 +1100 From: David Gibson To: Grant Likely Subject: Re: [PATCH] [POWERPC] get rid of `model = "UCC"' in the ucc nodes Message-ID: <20080208061451.GC26868@localhost.localdomain> References: <20080201150126.GB26545@localhost.localdomain> <72B60725-FB4A-42FA-832D-8FD5434B9042@kernel.crashing.org> <20080205132026.GE7983@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: Scott Wood , linuxppc-dev@ozlabs.org, Jon Loeliger List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Feb 05, 2008 at 09:39:02AM -0700, Grant Likely wrote: > On 2/5/08, David Gibson wrote: > > On Fri, Feb 01, 2008 at 09:23:47AM -0700, Grant Likely wrote: > > > cell-index has been useful for things like clock controllers to know > > > what offset into a shared clock control register or something like > > > that and a driver would pass the cell-index value to the shared reg > > > driver when requesting service. > > > > Right. Except that if the shared resource is just a single register, > > calling the routines to access it a "shared reg driver" gives a > > misleading impression. Depending on how the shared reg is used, even > > a lock may not be necessary, so potentially the drivers for the > > individual device instances using the shared resource can (safely) > > directly access it. > > Fair enough. In the case of a single shared, or a homogeneous set of > shared registers (all of them use the same index) I can see the > argument for cell index. Yes, that's the situation it was created for. > However, there are places where cell-index is being used where the > value of cell-index has no relation to the offset into a register. > But what about the case where the device uses multiple shared > registers, each one using a *different* offset. cell-index doesn't > describe this situation well (or at least no better than just using > the value of reg instead, a translation is still required) Absolutely. This is not a suitable situation in which to use cell-index. [snip] > >From booting-without-of (in the EMAC description): > - cell-index : 1 cell, hardware index of the EMAC cell on a > given ASIC (typically 0x0 and 0x1 for EMAC0 and EMAC1 on each Axon > chip. > > So, even if the intent was for cell-index to specify offsets into > shared regs, the description does not reflect that purpose. And > reading thorough the rest of the document, cell-index is described > purely in terms of enumerating ip blocks, so that is clearly the > assumption that people are making when using it. > > In other words, my point is this: *If* cell-index is just a way to > encode the manufacturing assigned ip-block number (EMAC0, EMAC1, etc) > then there is probably little or no value in it. The two arguments I > see for using cell-index in that mode are: > > 1) to offset into shared registers (but this doesn't hold because ip > block numbers often don't match register offsets and the reg property > would be just as suitable) > > 2) to logically identify ip blocks to the user (but cell-index was > never intended for this and /aliases is a better solution anyway) Right. The confusion arises because cell-index was invented on 4xx, where it's common practice to index global registers by the ip block number. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson