Re: [PATCH v16 2/7] power: add power sequence library

[Peter Chen]

On Tue, Jul 18, 2017 at 07:06:05PM +0200, Rafael J. Wysocki wrote:
> On Tue, Jul 18, 2017 at 6:29 AM, Peter Chen <hzpeterchen@xxxxxxxxx> wrote:
> > On Mon, Jul 17, 2017 at 03:39:07PM +0200, Rafael J. Wysocki wrote:
> >> > Sorry, I should describe more.
> >> >
> >> > Let's take USB bus as an example, when the new USB device is at the
> >> > host port, the device structure at device model is not created until
> >> > it is discoverable by the USB bus. If this new USB device needs to be
> >> > powered on before can be discoverable by the bus, the device structure
> >> > will be not created without powering on operation. The code usb_alloc_dev
> >> > (drivers/usb/core/usb.c) is only called for discoverable device.
> >> >
> >> > Unlike the other bus, eg, platform bus, it creates device structure
> >> > according to DT node. The USB bus was designed for hot plug model, the
> >> > device structure is for discoverable device. In recent years, we begin
> >> > to have some hard-wired USB device, Eg, onboard USB-hub, onboard USB 4G
> >> > Modem, etc at the market. It needs some board level power operation before
> >> > it can be found by the USB bus. This patch set is designed primarily for
> >> > fix this kind of problem. You will see at at pwrseq_generic.c, we use DT
> >> > version clock API of_clk_get and DT version gpio API of_get_named_gpio_flags
> >> > instead of device structure version, like devm_clk_get and
> >> > devm_gpiod_get_optional.
> >> >
> >> > MMC system has similar use case, it creates power sequence platform
> >> > device for this issue, but all those power stuffs (clock, gpio, etc)
> >> > may not be suitable as a dedicated virtual device at DT, they are belonged
> >> > to one physical device, so this patch set is created to see if this issue
> >> > can be fixed better.
> >>
> >> OK, thanks for the explanation.
> >>
> >> The above needs to be part of your problem statement.
> >
> > Ok, I will add it to cover letter.
> >
> >> >
> >> > The bus will power up all device nodes in this bus according to DT
> >> > information, the device structure has not created at this time.
> >>
> >> OK
> >>
> >> I still think that the information on power resources depended on by devices
> >> should be used for power management as well as for the initial power-up.
> >>
> >> The most straightforward way to arrange for that would be to make it possible
> >> to find the DT node matching the device after the device has been discovered
> >> and struct device created for it, say by USB.  That would require adding some
> >> more information on the device to the DT node, probably.
> >
> > After the device is created, the device node structure is under struct
> > device, say dev->of_node. The most difficulty for this issue is the
> > device creation is dynamic and is after the physical device is
> > discovered by the bus, the initial power-up is needed before the device
> > can be discovered by the bus.
> 
> So you power up all devices on the bus using the information from
> of_nodes upfront.
> 

I think your mean call pm_device_power_up(struct device *dev) for bus
level device (eg, USB HUB for USB), yeah, I can do that. But we still
have below problem:

Where we can put the kinds of power sequence implementation
(eg, pwrseq_generic.c) and the match mechanism between device
node and kinds of power sequence(eg, of_pwrseq_on at core.c)? These
stuffs can be shared among subsystems, and is better to use
one framework for it. MMC subsystem adds such things at its core
folder (drivers/mmc/core/pwrseq*) currently.

-- 

Best Regards,
Peter Chen