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

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Message-ID: <srhxu3r4sxy5ntx53nicf7l43sdjpiwavzd2qsgq2ovquzvt3u@cskcthmqznex>
Date: Tue, 14 Jan 2025 17:04:48 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Rob Herring <robh@...nel.org>
Cc: Bjorn Andersson <bjorn.andersson@....qualcomm.com>, 
	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>, 
	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 Tue, Jan 14, 2025 at 11:44:52AM -0600, Rob Herring wrote:
> 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?
> 

I presume so. What would the benefit of that be, over fixing up the
source asap?

Regards,
Bjorn