[PATCH] ARM: vexpress: initial device tree support

On Wed, 2011-09-21 at 15:57 +0100, Grant Likely wrote:

On Wed, Sep 21, 2011 at 7:24 AM, Rob Herring [off-list ref] wrote:

quoted

On 09/21/2011 04:19 AM, Dave Martin wrote:

quoted

      * arm,amba-bus -- widely used by other boards and patchsets, but
        seems not to be documented.

This should be dropped. There's not really any bus component to an amba
bus. All the probing info is within the primecell peripherals.

No, if it is an AMBA bus, then it is entirely appropriate to declare
it as an amba bus, but to also be compatible with "simple-bus".  In
fact, it would be better to use a compatible string that specifies the
specific implementation of AMBA bus since there are several versions
of the spec.

Dave asked me about details of the VE implementation. It's
sort-of-complicated... ;-)

1. Core talks to Static Memory Controller via AMBA (AXI)

   SOC { core --AXI--> SMC }

2. SMC generates transaction on Static Memory Bus talking to the IO FPGA

   tile/motherboard connector { SMC --SMB--> IOFPGA }

3. Now, depending on the device being accessed:

a) Transactions accessing SMSC9118, ISP1761, NOR Flash and PSRAM are
routed directly to the devices

   IOFPGA { SMB --> SMSC9118 et al. }

b) The rest of the traffic is converted back to AMBA (AHB/APB)
transactions and sent to the devices connected to internal AMBA matrix.

   IOFPGA { SMB --> AHB/APB bus master --AHB/APB--> PL180 }

I don't believe, though, that the DTS must reflect such level of
details. That's why I think that:

+       motherboard {
+               compatible = "simple-bus";

and

+               peripherals at 7,00000000 {
+                       compatible = "arm,amba-bus", "simple-bus";

is the best description of the reality :-)

Cheers!

Pawe?