linux-kernel - Re: [PATCH 6/7] ARM: dts: Add dts for Raspberry Pi 4 + Cirrus Logic Lochnagar2

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Date:   Thu, 15 Oct 2020 12:14:20 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        <broonie@...nel.org>, <robh+dt@...nel.org>
CC:     <patches@...nsource.cirrus.com>, <alsa-devel@...a-project.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-rpi-kernel@...ts.infradead.org>
Subject: Re: [PATCH 6/7] ARM: dts: Add dts for Raspberry Pi 4 + Cirrus Logic
 Lochnagar2


On 15/10/2020 11:25, Nicolas Saenz Julienne wrote:
> Hi Richard,
> your series is very welcome, upstream support for audio codecs on the RPi4 has
> always been lackluster.
> 
> Could you provide more information on the actual products? Are there custom
> made hats for the RPi4 or this wired into a generic development board.
> 
Info on the codecs is available from www.cirrus.com.
The Lochnagar audio development board is not a hat, but it can be wired
over to the RPi GPIO header. It is not specific to the RPi.

> On Wed, 2020-10-14 at 15:54 +0100, Richard Fitzgerald wrote:
>> This is based on the default bcm2711-rpi-4-b.dts.
> 
> Note that you could've included bcm2711-rpi-4.dts (as if it was a .dtsi).
> 
Ok, will change.

>> Configurations are provided for Cirrus Logic codecs CS42L92, CS47L15,
>> CS47L24, CS47L35, CS47L90 and WM8998.
>>
>> For each codec there is a sound node and a codec device node and both
>> default to disabled. Enable the pair for the codec in use.
>>
>> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
>> ---
> 
> Sadly I don't think creating a new device tree is a good solution here. If we
> were to do so for every RPi hat/usage it'd become unmanageable very fast. There
> is a way to maintain this in the open nonetheless. I suggest you build a DT
> overlay and submit it to https://github.com/raspberrypi/linux, see
> 'arch/arm/boot/dts/overlays.' The Raspberry Pi engineers have a kernel branch

We want something in mainline so that it can be used by people
developing on mainline and taken as a starting point for configuring
the codecs for other host platforms. The RPi is a convenient platform to
use as the base because it is widely available and low-cost.

> that tracks of the latest kernel release, so once you get the rest of patches
> sorted out and they are included in a release it'll make sense to do so.
> 
> I can't tell for other distros, but opensuse packages overlays, so the effort
> will ultimately be useful to users.
> 
> Regards,
> Nicolas
> 
>