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. > > 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 -- 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
