Hi Olav,

On Fri, Jun 27, 2014 at 11:23:27PM +0100, Olav Haugan wrote:

On 6/25/2014 2:18 AM, Will Deacon wrote:

quoted

Why can't it be dynamically detected? Whilst the StreamIDs are fixed in
hardware (from the SMMU architecture perspective), the SMRs are completely
programmable. Why doesn't something like Andreas's proposal work for you?
The idea there was to find the constant bits among the StreamIDs for a
master and create the mask accordingly.

Lets say I have an IOMMU with 2 masters and 2 SMRn slots with the
following stream IDs coming from the masters:

Master 1: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28
Master 2: 0x30

To make this work I would program SMR[0] with StreamID 0x20 and mask 0xF
to ignore lower 4 bits. SMR[1] would just be StreamID 0x30 with mask 0x0.

However, I could also have an IOMMU with 2 masters and 9 SMRn slots with
the following stream IDs:

Master 1: 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28
Master 2: 0x29

Here I would program all SMRn and leave the mask to be 0 for all SMRn's.
So how do I detect when to apply a mask or not?

You would aim to use the smallest number of SMRs per master possible.
You could probably use:

  Master 1: SMR[0].id == 0x20, SMR[0].mask = 0x07
            SMR[1].id == 0x28, SMR[1].mask = 0x00

  Master 2: SMR[2].id == 0x29, SMR[2].mask = 0x00

I am not familiar with Andreas's proposal. Do you have a link?

  http://marc.info/?l=linux-arm-kernel&m=139110598005846&w=2

Note that since Calxeda went under, Andreas is unfortunately no longer
working on this.

Will