Re: [PATCH v5 0/4] USB: misc: Add onboard_usb_hub driver

[Krzysztof Kozlowski]

On Wed, Feb 10, 2021 at 09:10:35AM -0800, Matthias Kaehlcke wrote:
> This series adds the onboard_usb_hub_driver, the corresponding
> device tree bindings and creation of onboard_usb_hub platform in
> the xhci-plat driver during probe().
> 
> The main issue the driver addresses is that a USB hub needs to be
> powered before it can be discovered. For discrete onboard hubs (an
> example for such a hub is the Realtek RTS5411) this is often solved
> by supplying the hub with an 'always-on' regulator, which is kind
> of a hack.

It seems you are re-developing the power sequence drivers which perform
exactly this. Peter Chen some time ago was bringing power sequence to
USB devices, but I lost track where this ended up.

Some of his (and my) very old work (2017...) can be found here:
https://github.com/krzk/linux/tree/wip/odroid-u3-usb3503-pwrseq

Instead of adding custom driver hiding some USB hub implementation,
power sequence seems a generic solution. What if you need to power cycle
other embedded USB device? Not a hub?

I was not aware of previous discussions so maybe I am repeating
someone.

Best regards,
Krzysztof