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

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Message-ID: <ZV3OgorG4G4mwvv1@hovoldconsulting.com>
Date:   Wed, 22 Nov 2023 10:48:50 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Felipe Balbi <balbi@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
Subject: Re: [PATCH 00/12] usb: dwc3: qcom: Flatten dwc3 structure

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