Re: [PATCH v2 1/4] dt-bindings: bluetooth: add new wcn3991 compatible to fix bd_addr

From: Doug Anderson <dianders@google.com>
To: Johan Hovold <johan@kernel.org>
Cc: Rob Herring <robh@kernel.org>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	 Johan Hovold <johan+linaro@kernel.org>,
	Marcel Holtmann <marcel@holtmann.org>,
	 Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	 Johan Hedberg <johan.hedberg@gmail.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	 Bjorn Andersson <quic_bjorande@quicinc.com>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	 linux-bluetooth@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	 netdev@vger.kernel.org, devicetree@vger.kernel.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/4] dt-bindings: bluetooth: add new wcn3991 compatible to fix bd_addr
Date: Mon, 18 Mar 2024 08:26:26 -0700	[thread overview]
Message-ID: <CAD=FV=UpuD7Lq0DxSZAGpL4Mi2uxy9HNt3V3FZq7Y3p--gbMrg@mail.gmail.com> (raw)
In-Reply-To: <ZfhZffrZXwtKgZ13@hovoldconsulting.com>

Hi,

On Mon, Mar 18, 2024 at 8:10 AM Johan Hovold <johan@kernel.org> wrote:
>
> > > I wanted to avoid doing this, but if we have to support Google's broken
> > > boot firmware for these devices, then this is how it needs to be done.
> >
> > Don't Chromebooks update everything together. So maybe we don't care in
> > this case?
>
> That was my hope, but Matthias seemed to suggest that we need to
> continue supporting the current (broken) binding because doing such a
> coordinated update may be easier said than done:
>
>         https://lore.kernel.org/lkml/ZcuQ2qRX0zsLSVRL@google.com/

Chromebooks update kernel and devicetree together, but not firmware.
Firmware is relatively hard to get updated trying to have kernel and
firmware updates coordinated at the exact same time has challenges.
This would further be complicated by the fact that firmware
qualification for each variant happens on its own timeline.

> A new compatible string (or one-off property) would allow them do make a
> change when they are ready (e.g. by only updating the devicetrees after
> all boot firmware has been patched and pushed out).

I have no real opinion about the exact way this is solved so happy to
let DT folks decide on how they want this. I will note, however, that
device trees are never shipped separately and thus we have no
intrinsic need for DT backward compatbility here. It would be OK from
a ChromeOS perspective to add a property or compatible string for the
broken case.

-Doug