The problem is that the tft driver currently in mainline assumes that the dcr control registers are accessed through mmio, and probes for a reg=<> property. Since the device is actually a dcr device, it can be connected via mmio through a bride, or to the native dcr bus of the processor. For the time being, I'd like to generate device trees compatible with either mechanism.
so, the problem is that the tree-parents of the tft node all have ranges, and if the dcr-parent of the node is a bridge, then it has a reg=<> property, But if the dcr-parent is also a tree-parent, then it has to have ranges; and a reg=<> property, which seems very strange, and not something I think is a good thing to do. Steve -----Original Message----- From: David Gibson [mailto:[EMAIL PROTECTED] Sent: Wed 5/7/2008 6:59 PM To: Stephen Neuendorffer Cc: Grant Likely; linuxppc-dev@ozlabs.org Subject: Re: [PATCH 4/4] [POWERPC] Xilinx: Framebuffer: Usedcrinfrastructure. On Tue, May 06, 2008 at 10:43:50AM -0700, Stephen Neuendorffer wrote: [snip] > > > Hmmm, something doesn't quite feel right about this. The node > > > describing the tft device is a child of the [EMAIL PROTECTED] node which > > > is the > > > dcr bus. However, dcr bindings use dcr-bus and dcr-reg instead of > > > parent-child relationship to specify how to access the dcr > registers. > > > So, in this example; if the device is described by [EMAIL PROTECTED], and > > > the > dcr > > > bus is described by [EMAIL PROTECTED], then what does [EMAIL PROTECTED] > > > describe? (I do understand what they really describe in EDK terms; > > > but I'm looking at it through device tree glasses). > > > > > > I don't think the presence of a [EMAIL PROTECTED] node is a problem, but > > > in this > > > case #size/address-cells doesn't have any meaning (the child doesn't > > > have a reg property) and it looks like it should be a child of the > > > opb2dcr-bridge node (otherwise, what is it attached to?). > > > > Yes, indeed. If [EMAIL PROTECTED] is representing the DCR bus / interface > > it > > should really have the dcr-access-method property and have all the > > dcr-parent handles point at it. > > Hmm, I tend to agree. Certainly the address-cells and size-cells can > go. Part of the nastiness is that I'm trying to maintain a modicum of > backward compatibility at the moment in the device tree generator. This > structure allow the [EMAIL PROTECTED] node to have ranges; and the tft node > to have > a properly translated reg = <> property for the existing driver which > only understands mmio. I don't think it really works for the opb2dcr > bridge to be a bridge and a dcr-controller at the same time. :) This > structure is also very similar to what is generated if the > dcr-controller is native from the processor (there's just no bridge). I don't really understand what you're getting at here, sorry. Perhaps you could describe what you're doing with the tft device in more detail? > > Current standard practice is not to represent the DCR bus as node with > > subnodes for the DCR-controlled devices. That's because the DCR bus > > tends to run in addition to other on-chip busses, and some things have > > to go on another on-chip bus to make sense, but still have DCR control > > registers (for example the internal bus bridges on 4xx). > > > > Arguably for DCR-only devices we should instead have a node > > representing the DCR bus and just put the devices under it with the > > DCR number encoded in reg in the normal way. But then its > > inconsistent with the devices that need the other DCR representation. > > Yup, it's exactly this problem I'm trying to fix in the case of the tft > driver. -- 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
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