Re: [PATCH v2 07/10] ARM: tegra: pcie: Add device tree support

On 06/13/2012 12:34 AM, Thierry Reding wrote:

* Stephen Warren wrote:

...

quoted

I think you also need a property to specify the exact port
layout; the Tegra20 controller supports:

1 x4 port 2 x2 ports (you can choose to use only 1 of these I
assume)

So just because only 1 of the ports is enabled, doesn't imply
it's x4; it could still be x2.

Tegra30 has more options.

Both the upstream and downstream drivers currently hard-code this
to dual and 411 (I assume that means 1x4, 2x1?) configurations for
Tegra20 and Tegra30 respectively. Unfortunately the register
AFI_PCIE_CONFIG isn't documented on Tegra20 at all and for Tegra30
lists only the valid configurations (see 28.4.1.5 PCIe CONFIG) but
not the corresponding encodings.

Maybe a good name for the new property would be "num-lanes". I also
wonder if this property would be better off in the parent node,
which would make it easier to check for valid configurations.
Otherwise the code would have to collect the settings of all the
ports and check if the combination is valid. Then again, having
num-lanes in the parent with one cell for each controller isn't
very nice if each controller can be individually disabled.

Indeed, since the register that controls this is in the main register
set rather than the per-port register set, it does seem like a good
idea to put the property in the main node, not the per-port node.