linux-kernel - Re: [PATCH 1/2] dt-bindings: net: broadcom-bluetooth: Add property for autobaud mode

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Date:   Thu, 5 May 2022 16:13:26 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Hakan Jansson <hakan.jansson@...ineon.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: net: broadcom-bluetooth: Add property
 for autobaud mode

On Thu, May 5, 2022 at 3:11 PM Hakan Jansson <hakan.jansson@...ineon.com> wrote:

> I suppose a general flag could be useful but to be honest I don't know
> if any other devices besides the ones using the Broadcom driver has any
> use for it. You would probably also still want to be able to use
> current-speed to set the link speed and end up using both
> current-speed=x and current-speed-auto at the same time, which might
> look a little confusing?

I do not think it is more confusing than being able to use
current-speed and brcm,uses-autobaud-mode at the same time.

> Please let me know if you'd still prefer "current-speed-auto" over
> "brcm,uses-autobaud-mode" and I'll revise the patch and rename it!

It actually depends a bit.

This:

> >> +      The controller should be started in autobaud mode by asserting
> >> +      BT_UART_CTS_N (i.e. host RTS) during startup. Only HCI commands supported
> >> +      in autobaud mode should be used until patch FW has been loaded.

sounds a bit vague?

Does it mean that CTS is asserted, then you send a bit (CTS then goes low)
and then CTS is asserted again when the device is ready to receieve more
data? i.e is this some kind of one-bit mode, because it doesn't sound like
it is using CTS as it was used in legacy modems.

Some more explanation of this mode is needed so we can understand if
this is something generic or a BRCM-only thing.

Yours,
Linus Walleij