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From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Date: Mon, 18 Mar 2024 16:17:24 +0200
Message-ID: <CAA8EJpoxq6__DMcsuAEsnxBfPrrQBuu4ZgfULkok4KWSYVxuHQ@mail.gmail.com>
Subject: Re: [PATCH v2 1/4] dt-bindings: bluetooth: add new wcn3991 compatible
 to fix bd_addr
To: Johan Hovold <johan@kernel.org>
Cc: Johan Hovold <johan+linaro@kernel.org>, Marcel Holtmann <marcel@holtmann.org>, 
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>, Rob Herring <robh+dt@kernel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>, 
	Johan Hedberg <johan.hedberg@gmail.com>, Matthias Kaehlcke <mka@chromium.org>, 
	Doug Anderson <dianders@google.com>, 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
Content-Type: text/plain; charset="UTF-8"

On Mon, 18 Mar 2024 at 15:17, Johan Hovold <johan@kernel.org> wrote:
>
> On Mon, Mar 18, 2024 at 03:00:40PM +0200, Dmitry Baryshkov wrote:
> > On Mon, 18 Mar 2024 at 13:09, Johan Hovold <johan+linaro@kernel.org> wrote:
> > >
> > > Several Qualcomm Bluetooth controllers lack persistent storage for the
> > > device address and instead one can be provided by the boot firmware
> > > using the 'local-bd-address' devicetree property.
> > >
> > > The Bluetooth bindings clearly says that the address should be specified
> > > in little-endian order, but due to a long-standing bug in the Qualcomm
> > > driver which reversed the address some bootloaders have been providing
> > > the address in big-endian order instead.
> > >
> > > The only device out there that should be affected by this is the WCN3991
> > > used in some Chromebooks. To maintain backwards compatibility, mark the
> > > current compatible string as deprecated and add a new
> > > 'qcom,wcn3991-bt-bdaddr-le' for firmware which conforms with the
> > > binding.
>
> > This compatible doesn't describe new hardware kind. As such, I think,
> > the better way would be to continue using qcom,wcn3991-bt compatible
> > string + add some kind of qcom,bt-addr-le property.
>
> No, you can't handle backwards compatibility by *adding* a property.
>
> 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.

One hardware compat string per hardware type.

-- 
With best wishes
Dmitry