Re: [PATCH 00/12] usb: dwc3: qcom: Flatten dwc3 structure

Johan Hovold
2023-11-22T09:48:36Z

On Mon, Oct 16, 2023 at 08:11:08PM -0700, Bjorn Andersson wrote:
> The USB IP-block found in most Qualcomm platforms is modelled in the
> Linux kernel as 3 different independent device drivers, but as shown by
> the already existing layering violations in the Qualcomm glue driver
> they can not be operated independently.
>
> With the current implementation, the glue driver registers the core and
> has no way to know when this is done. As a result, e.g. the suspend
> callbacks needs to guard against NULL pointer dereferences when trying
> to peek into the struct dwc3 found in the drvdata of the child.
>
> Missing from the upstream Qualcomm USB support is handling of role
> switching, in which the glue needs to be notified upon DRD mode changes.
> Several attempts has been made through the years to register callbacks
> etc, but they always fall short when it comes to handling of the core's
> probe deferral on resources etc.

Nice to see this finally being worked on. It's not clear why mode-change
notifications would be a problem though, as if you get such a
notification, you know that core has been probed.

> Furhtermore, the DeviceTree binding is a direct representation of the
> Linux driver model, and doesn't necessarily describe "the USB IP-block".

True.

Johan