On 07/31/2012 07:26 AM, Stephen Warren wrote:
On 07/30/2012 09:44 AM, Rob Herring wrote:
On 07/27/2012 07:05 AM, Alexandre Courbot wrote:
Some device drivers (panel backlights especially) need to follow precise
sequences for powering on and off, involving gpios, regulators, PWMs
with a precise powering order and delays to respect between each steps.
These sequences are board-specific, and do not belong to a particular
driver - therefore they have been performed by board-specific hook
functions to far.
With the advent of the device tree and of ARM kernels that are not
board-tied, we cannot rely on these board-specific hooks anymore but
need a way to implement these sequences in a portable manner. This patch
introduces a simple interpreter that can execute such power sequences
encoded either as platform data or within the device tree.
Why not? We'll always have some amount of board code. The key is to
limit parts that are just data. I'm not sure this is something that
should be in devicetree.
Perhaps what is needed is a better way to hook into the driver like
notifiers?
I would answer that by asking the reverse question - why should we have
to put some data in DT, and some data into board files still?
I'd certainly argue that the sequence of which GPIOs/regulators/PWMs to
manipulate is just data.
To be honest, if we're going to have to put some parts of a board's
configuration into board files anyway, then the entirety of DT seems
useless; I'd far rather see all the configuration in one cohesive place
than arbitrarily split into two/n different locations - that would make
everything harder to maintain.
Also, having these sequences into the DT would allow an older kernel to
boot on and correctly initialize a newer board with - which is also part
of the DT's purpose if I am not mistaken.
Alex.
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