Re: [edk2-devel] Additional configuration options on Armada/Cn913x

[greg@unrelenting.technology]

June 11, 2020 4:19 PM, "Ard Biesheuvel" <ard.biesheuvel@arm.com> wrote:

> On 6/5/20 5:19 PM, Marcin Wojtas via groups.io wrote:
> 
>> Hi,
>> I'd like to ask for comments before I develop the actual code - > currently we have 2 workarounds
>> done specifically for Linux:
>> a. ECAM shift in PCIE
>> b. SPCR address space definition
> 
> What does this mean?

The SPCR in upstream edk2 is set up to work around some Linux weirdness (?) and I have to do this:

https://github.com/myfreeweb/edk2-platforms/commit/74ec98a6498e78d2ae6c861db88487bf75f2e1a1

to make it work on FreeBSD.

>> Both above are not needed e.g. in FreeBSD and I was requested to add > their optional disabling.
> 
> Disabling ECAM shift is just a matter of exposing the iATU controls to the OS, right? Why do you
> need to disable it?

I'm not sure what iATU controls are (and we don't want to do anything in the OS),
but basically the current address is shifted by 0x8000 to only expose the last device to the OS,
to work around the silicon bug (lack of some filtering thing) that causes devices to appear many many times.

But actually most modern devices (e.g. AMD RX 480, Mellanox CX2) *do not* get duplicated at all, they show up
in the first position, and this shift moves the memory way past that position and the OS sees
no PCIe devices at all. The only device that was duplicated into all slots for me was a cheap SATA card.

In my experience whether the device is duplicated seems to correlate with the "Legacy" field
in the UEFI Shell's pci command. IIRC Marcin has explained the actual technical characteristic
of these devices in some mail before. So it might actually be possible to decide whether to do the shift
automatically at runtime depending on the inserted device (?)
But a setting in the setup menu is easier to do and less magical.

I've just been running with the shift reverted:

https://github.com/myfreeweb/edk2-platforms/commit/36395be2a8707f6d396e07405eb9fe47b64cf964

to make my Radeon GPU work.