[U-Boot] PCIe support for Tegra T30 ?

[Thierry Reding <thierry.reding@gmail.com>]

On Fri, Jul 05, 2013 at 11:19:04AM -0600, Stephen Warren wrote:
> On 07/05/2013 08:41 AM, Bob Koninckx wrote:
> > Hi,
> > 
> > Are there any plans for adding PCIe support for Tegra T30 SoC in the
> > near future? If not, what would it take if we would want to do this
> > ourselves. Any pointer in the right directions would be greatly
> > appreciated.
> 
> I don't believe anyone is actively working on this at present. It would
> be great to have this support in place.
> 
> If you want to take a crack at it yourself, I suggest the following
> resources:
> 
> Thierry Reding has recently created a new PCIe driver for Tegra in the
> Linux kernel. You can find this as part of:
> 
> git://gitorious.org/thierryreding/linux.git next
> 
> The downstream U-Boot port for the Tegra20 TrimSlice board has PCIe
> support, for the built-in NIC. You can find that at:
> 
> git://gitorious.org/trimslice-u-boot/trimslice-u-boot.git master

The Tegra PCIe driver in that repository looks very similar to what's
currently in Linux, that is before the major rework that will hopefully
be merged for 3.12.

One of the bigger things missing for that driver is regulator support.
CompuLab made it very easy to use PCIe with TrimSlice because they
didn't hook it up to a PMU (unlike every reference design). The downside
of that is that they didn't have to write any code to enable the
regulators and chances are that your design needs that. I'm also not
aware of any ongoing efforts within U-Boot to provide a regulator
framework. drivers/power seems where most PMU-like devices currently
have their drivers, but there's no generic API to use them.

To remedy that situation I think we have two options: one is to add such
a framework and the other alternative is to provide board-level hooks to
add hook into the PMU. The latter is sort of ugly and won't play very
nicely with DT. The former will be a bit more work. But perhaps you
don't need regulator support for the particular hardware that you use.

The other thing that TrimSlice's U-Boot doesn't provide is DT support.
Most of the Tegra drivers have been moved over to being controlled via
the device tree so I assume that PCIe will have to be as well?

I would personally very much like to see PCIe support for Tegra in
U-Boot, so if there's anything I can do to help, please feel free to
ask.

Thierry
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