On Friday, February 03, 2017 04:16:15 PM Peter Chen wrote:

On Wed, Feb 01, 2017 at 09:08:17AM +0100, Greg Kroah-Hartman wrote:

quoted

On Wed, Feb 01, 2017 at 12:10:17AM +0100, Rafael J. Wysocki wrote:

quoted

On Tue, Jan 3, 2017 at 7:33 AM, Peter Chen [off-list ref] wrote:

quoted

We have an well-known problem that the device needs to do some power
sequence before it can be recognized by related host, the typical
example like hard-wired mmc devices and usb devices.

This power sequence is hard to be described at device tree and handled by
related host driver, so we have created a common power sequence
library to cover this requirement. The core code has supplied
some common helpers for host driver, and individual power sequence
libraries handle kinds of power sequence for devices. The pwrseq
librares always need to allocate extra instance for compatible
string match.

pwrseq_generic is intended for general purpose of power sequence, which
handles gpios and clocks currently, and can cover other controls in
future. The host driver just needs to call of_pwrseq_on/of_pwrseq_off
if only one power sequence is needed, else call of_pwrseq_on_list
/of_pwrseq_off_list instead (eg, USB hub driver).

For new power sequence library, it can add its compatible string
to pwrseq_of_match_table, then the pwrseq core will match it with
DT's, and choose this library at runtime.

Signed-off-by: Peter Chen <redacted>
Tested-by: Maciej S. Szmigiero <redacted>
Tested-by Joshua Clayton [off-list ref]
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Tested-by: Matthias Kaehlcke <mka@chromium.org>

Quite honestly, I have a really hard time with trying to follow this
code and the total lack of documentation makes it even harder. 

Sorry about that, Is it ok I add the design doc at:
Documentation/power/power-sequence/design.rst?

You can do that if you think it will address the request to explain the design.

quoted

quoted

particular, the generic power sequence code is not even commented at
all, 

The generic power sequence code just implements the APIs which are 
called at power/pwrseq/core.c, and those API are commented at
include/linux/power/pwrseq.h. Anyway, I will add more comments at it.

It actually seems to be doing more than that and I'm not sure why the code in
core.c is necessary at all.  The "generic" thing seems to be the only user of
it anyway and the callbacks seem to be tailored to its needs.

Thanks,
Rafael