Re: [RFC V2] OPP: Redefine bindings to overcome shortcomings

On 29 January 2015 at 21:12, Rob Herring [off-list ref] wrote:

On Wed, Jan 28, 2015 at 7:39 PM, Viresh Kumar [off-list ref] wrote:

quoted

The goal is to choose the driver which we want to probe for a platform. There
can be multiple DT enabled cpufreq drivers present in a build and the platform
needs some way to choose one of them.

That was not my original thought, but rather it is versioning the
binding and a way to find OPP nodes. That doesn't mean we can't do
things to make it easier to match to drivers.

Okay.

quoted

For example, if both cpufreq-dt, exynos-cpufreq and arm-big-little drivers are
present in a kernel build, the how do we specify which one a platform wants to
use.

What does the exynos driver do that the other 2 don't?

There are efforts going on to start using cpufreq-dt instead
of exynos drivers. So, they might die at some point of time.

Anyway, there can be cpufreq drivers which co-exist
cpufreq-dt, even if they are parsing the same bindings.

I will likely nak any such strings that are solely there to match to
these 2 drivers. The information is there in DT already. It's just not
a single property to match on. You can tell it is a big.LITTLE system
by the fact your have 2 different cpu types. You can use the top level
compatible strings when you need a machine specific driver. I would
not be trying to get cpufreq platform devices to be created by
of_platform_populate. The other issue I have is you may not always
have 2 drivers for bL and non-bL. Really symmetric multi-cluster or
single cluster should be a subset of functionality of bL.

I think you just need to have an initcall which does this:

if (of_find_matching_node_and_match(machine_specific_driver_match list))
  platform_device_create(match->data);
else if (is_big_little() && has_opp)
  platform_device_create(big_little_device);
else if (has_opp)
  platform_device_create(cpufreq_dt_device);

Or perhaps you handle the generic ones late in boot only if no machine
specific driver has been probed. There is no generic solution ATM for
selecting the best driver when there are multiple matches.

One thing is clear. The compatibility string here isn't going to be
like what I had in mind. So, let it just define the versioning
here and I will see how can I solve the driver-probe problem.
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