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. Then you scan the bus and discover devices. For each of them, once it has been discovered, you look up a matching of_node and initialize power_state from there. >> >> 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. Right. So you do the power up upfront, as per the above. Thanks, Rafael -- 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
