On 25/11/2013 16:34, Linus Walleij wrote:
On Wed, Nov 20, 2013 at 1:02 AM, Kyungmin Park <kmpark@xxxxxxxxxxxxx> wrote:
On Wed, Nov 20, 2013 at 4:16 AM, Stephen Warren <swarren@xxxxxxxxxxxxx> wrote:
I think that last point should be addressed by having a driver that owns
the GPIO set it to the desired output level, and the implementation of
Some pins are not connected (NC). At that cases, there's no drivers to
handle it. To reduce power leakage, it sets proper configuration with
values instead of reset values.
This is correspondant to the PIN_CONFIG_OUTPUT from
include/linux/pinctrl/pinconf-generic.h
Indeed it is - I was waiting for someone to point that out. Now we've
got there...
I've been working on extending the shmobile PFC driver to provide
"gpio-mode" and implement PIN_CONFIG_OUTPUT as described by
Documentation/pinctrl.txt, primarily to handle sleep states, but I have
begun to wonder about the initial state problem, as discussed here.
As far as I can see, we can't currently specify "fallback" states for
pins, which is one of Tomasz' key requirements.
We can specify "hog" states, and we can specify "default for a driver",
but not "default before/in absence of a driver" or "sleep in absence of
a driver". Having a hog precludes any finer driver control, AFAICT.
Some of our existing pre-pinconf board files have a "unused pins" table
which is used to claim and pull GPIOs. I've converted that to "hog"
pinconf, but that only works because the table omits all pins used by
drivers. And, unsurprisingly, that's been error-prone; if those tables
originally covered all unused pins, they don't any more.
I'd like confidence that we can get every pin into the correct state by
having a fully-populated table containing all pins, that can be used
regardless of which drivers start. I think what we're lacking is a "weak
hog". Whatever you call that. :)
That would also specify the state to fallback to when a group is
released (where we currently do pinmux_disable_setting).
Thoughts?
Kevin
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