On Fri, Feb 03, 2017 at 10:14:31PM +0100, Rafael J. Wysocki wrote: > 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: > > > On Wed, Feb 01, 2017 at 12:10:17AM +0100, Rafael J. Wysocki wrote: > > > > On Tue, Jan 3, 2017 at 7:33 AM, Peter Chen <peter.chen@xxxxxxx> wrote: > > > > > 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 <peter.chen@xxxxxxx> > > > > > Tested-by: Maciej S. Szmigiero <mail@xxxxxxxxxxxxxxxxxxxxx> > > > > > Tested-by Joshua Clayton <stillcompiling@xxxxxxxxx> > > > > > Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > > > > > Tested-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > > > > > > > > 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. > > > > > 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. > Currently, the "generic" pwrseq is the only use case. But some devices may have custom power sequence [1], and MMC devices (mmc card/wifi) have two power sequences (drivers/mmc/core/pwrseq_emmc.c, drivers/mmc/core/pwrseq_simple.c) I have an example use case at v7 named pwrseq_compatible_sample.c for those custom use case [2]. [1] https://www.spinics.net/lists/devicetree/msg139756.html [2] https://lkml.org/lkml/2016/9/19/972 -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
