On Mon, Jul 17, 2017 at 03:39:07PM +0200, Rafael J. Wysocki wrote:

quoted

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.

quoted

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.

Then, the DT device nodes would be used for the initial power-up and next, after
discovering a device, you'd do a lookup in the DT, find the node matching it
and read the power resuources information from there to populate the device's
power state structure.  From that point on you can simply use the interface I
suggested.

Just like I said above, without initial power-up, the device can't be
discovered by the bus.

-- 

Best Regards,
Peter Chen