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

[Johan Hovold]

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@xxxxxxxxxx> 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.

Johan