On Tue, Aug 26, 2014 at 10:04:33AM +0200, Thierry Reding wrote:

quoted

quoted

No. simplefb just wants to write to some memory that hardware has been
set up to scan out. The platform requires that the clocks be on. Other
platforms may not even allow turning off the clocks.

Like what? the rpi? Come on. Just because the videocore is some black
box we know nothing about doesn't mean we should use it as an example.

You make it sound like the Raspberry Pi is somehow less important than
sunxi.

No. What I mean is that it seems like we are somehow punished, or at
least blamed, for having a better and more complete kernel support.

quoted

Any decent enough SoC, with a decent support in the kernel will have
clocks for this, and I really wonder how simplefb will behave once its
clocks will be turned off...

There are other devices besides ARM SoCs that may want to use this
driver and that don't have clock support.

And in this case, with this patch, simplefb will not claim any clock,
nor will fail probing.

But you're missing my point. What I'm saying is that the simplefb driver
is meant to serve as a way to take over whatever framebuffer a firmware
set up. Therefore I think it makes the most sense to assume that nothing
needs to be controlled in any way since already been set up by firmware.
Eventually there should be a driver that takes over from simplefb that
knows how to properly handle the device's specifics, but that's not
simplefb.

I guess such a hand over if it were to happen in the kernel would
involve the second driver claiming the resources before the first one
release them. How is that different in this case?

The goal of this patch series is to keep clocks from being turned off.
But that's not what it does. What it does is turn clocks on to prevent
them from being turned off. In my opinion that's a workaround for a
deficiency in the kernel (and the firmware/kernel interface) and I think
it should be fixed at the root. So a much better solution would be to
establish a way for firmware to communicate to the kernel that a given
resource has been enabled by firmware and shouldn't be disabled. Such a
solution can be implement for all types of resources and can be reused
by all drivers since they don't have to worry about these details.

Mike Turquette repeatedly said that he was against such a DT property:
https://lkml.org/lkml/2014/5/12/693

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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