On 30/11/2021 00.02, Rob Herring wrote:
Sure, it just means I have to reinvent the PCI capability lookup wheel
again. I'd love to use the regular accessors, but the infrastructure
isn't up to the point where we can do that yet yere. DWC also reinvents
this wheel, but we can't reuse that code because it pokes these
registers through a separate reg range, not config space (even though it
seems like they should be the same thing? I'm not sure what's going on
in the DWC devices... for the Apple controller it's just the ECAM).
Since it is just ECAM, can you use the regular config space accessors?
The problem is this is before the PCI objects are created, so those
wouldn't work since they expect to be called on a pci_dev and such.
+ max_gen = of_pci_get_max_link_speed(port->np);
+ if (max_gen < 0) {
+ dev_err(port->pcie->dev, "max link speed not specified\n");
Better to fail than limp along in gen1? Though you don't check the
return value...
Usually, the DT property is there to limit the speed when there's a
board limitation.
The default *setting* is actually Gen4, but without
PCIE_LINK_WIDTH_SPEED_CONTROL poked it always trains at Gen1. Might make
more sense to only set the LNKCTL field if max-link-speed is specified,
and unconditionally poke that bit. That'll get us Gen4 by default (or
even presumably Gen5 in future controllers, if everything else stays
compatible).
You already do some setup in firmware for ECAM, right? I think it
would be better if you can do any default setup there and then
max-link-speed is only an override for the kernel.
I thought the PCIE_LINK_WIDTH_SPEED_CONTROL thing had to be set later,
but trying it now I realized we were missing a bit of initialization
that was causing it not to work. Indeed it can be done there and we can
drop it from the kernel.
We could even do the max-link-speed thing in m1n1 if we want. It has
access to the value from the ADT directly, which to be correct we'd have
to dynamically transplant to the DT, since there's at least one device
that has different PCIe devices on one port depending on hardware
variant, while sharing a devicetree. If we're okay with the kernel just
not implementing this feature for now, we can say it's the bootloader's job.
Ultimately we ship the DTs along with m1n1, so there's an argument that
if some day we need to override the max-link-speed for whatever reason
over what the ADT says, well, we'd be shipping the updated DT along with
m1n1 anyway, so we might as well make m1n1 do it... if so, it might make
sense to drop those properties from the actual DTs we ship altogether,
at least for now.
If we decide to make it m1n1's job entirely, we can drop this patch
altogether, at least for now (I can't say how this will interact with
suspend/resume and other power management, and hotplug... but we'll open
that can of worms when we get there).
--
Hector Martin (marcan@xxxxxxxxx)
Public Key: https://mrcn.st/pub
