linux-kernel - Re: [PATCH v3 00/12] usb: dwc3: qcom: Flatten dwc3 structure

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Message-ID: <20250114174452.GB1414434-robh@kernel.org>
Date: Tue, 14 Jan 2025 11:44:52 -0600
From: Rob Herring <robh@...nel.org>
To: Bjorn Andersson <bjorn.andersson@....qualcomm.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Felipe Balbi <balbi@...nel.org>,
	Wesley Cheng <quic_wcheng@...cinc.com>,
	Saravana Kannan <saravanak@...gle.com>,
	Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>, Frank Li <Frank.li@....com>,
	linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 00/12] usb: dwc3: qcom: Flatten dwc3 structure

On Mon, Jan 13, 2025 at 09:11:33PM -0800, 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 proper 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.
> 
> Furhtermore, the DeviceTree binding is a direct representation of the
> Linux driver model, and doesn't necessarily describe "the USB IP-block".
> 
> This series therefor attempts to flatten the driver split, and operate
> the glue and core out of the same platform_device instance. And in order
> to do this, the DeviceTree representation of the IP block is flattened.
> 
> To avoid littering the dwc3-qcom driver with the migration code - which
> we should be able to drop again in a LTS or two - this is now placed in
> drivers/of/overlays.
> 
> A patch to convert a single platform - sc8280xp - is included in the
> series. The broader conversion will be submitted in a follow up series.

Is it not possible to use the same overlays also fixup the .dts files at 
build time?

Rob