[PATCH 3/3] ARM: l2x0: Add OF based initialization

Hi,

On Tue, Jun 7, 2011 at 9:54 AM, Rob Herring [off-list ref] wrote:

Olof,

On 06/07/2011 11:20 AM, Olof Johansson wrote:

quoted

On Tue, Jun 7, 2011 at 7:22 AM, Rob Herring[off-list ref] ?wrote:

quoted

+- aux-value : Value to set the Auxillary Control register to. Setting
masked
+ ?bits is undefined. Default value is 0.
+- aux-mask : Mask of bits to preserve in the Auxillary Control register.
+ ?Default value is 0xffffffff.

The device tree should describe the hardware, not the way the linux
kernel drives the hardware. In the case of the AUX register, it's
mostly a collection of options that are either turned on or off. I
don't think they should necessarily be described as an opaque 32-bit
word, but instead as separate attributes.

Unfortunately, the meaning of the bits depends on the model and there
doesn't seem to be any commonality or subset of options as to what each
platform is setting up.

Luckily, the meaning of the bits can be derived from the most-specific
compatible string, but yeah, it seems like many SoC vendors choose to
enable different settings. Likely because of either what has been
verified to work well, or what worked well for some benchmarks that
they cared about enough to optimize the default case for.

quoted

At least the geometry should be specified that way.

That's probably the only part that doesn't get changed. :)

Yep, it should ideally still be described though.

quoted

For feature enable bits, it depends on what features should be enabled
and from the kernel side. I'm not sure that belongs in the device tree
at all.

I don't think it can be decided what the kernel needs to setup by the device
tree. The main reason it's needed in the kernel at all is probably because
the bootloader didn't setup aux_ctrl or set it up incorrectly.

Perhaps the magic values should just be left in the platforms and continue
to be passed into the OF init function:

l2x0_of_init(__u32 aux_val, __u32 aux_mask);

This might be the least painful way to do it, agreed.

If a specific platform wants to have firmware pass in the preferred
values, they could do so through /chosen or similar.


-Olof