linux-kernel - Re: [PATCH 0/2] ARM: dts: bcm-mobile: Split out nodes used by both BCM21664 and BCM23550

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Date: Sat, 8 Jun 2024 15:06:22 +0200
From: Stanislav Jakubek <stano.jakubek@...il.com>
To: Artur Weber <aweber.kernel@...il.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Ray Jui <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	~postmarketos/upstreaming@...ts.sr.ht, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] ARM: dts: bcm-mobile: Split out nodes used by both
 BCM21664 and BCM23550

Hi Artur,

thanks for the patches! Some notes below.

On Wed, Jun 05, 2024 at 08:40:11AM +0200, Artur Weber wrote:
> The BCM21664 and BCM23550 are nearly identical to each other in terms
> of register layout. This was verified against a downstream kernel[1] -
> Broadcom's kernel has "RDB" directories which includes headers with
> the full register maps for the included hardware. Running:
> 
>   diff --recursive arch/arm/mach-{hawaii,java}/include/mach/rdb
> 
> reveals that the differences are minuscule - some things related to
> ISP and H264 decoding. Most of the other differences are related to
> the different CPUs in the two chipsets - the BCM21664 has 2x Cortex-A9
> cores, and the BCM23550 has 4x Cortex-A7 cores.
> 
> In mainline, most drivers are also re-used between the two.
> 
> To make development for both platforms easier, split out the common
> nodes into a separate DTSI, bcm21664-common.dtsi. This only leaves
> the device-specific nodes - so, CPU and related things - in the SoC-
> specific DTSIs (bcm21664.dtsi and bcm23550.dtsi).

The name "bcm21664-common" makes me think that it's a DTSI for common
properties of multiple BCM21664 *board* DTs, which is obviously not the
case here. IMO something like "bcm21664-bcm23550-common" makes more sense here.

> 
> The new DTSI is based off the bcm23550.dtsi, with its split into
> busses. Since it's pretty much 99% identical, I kept the licensing
> of the original file (BSD 3-clause). The license for the bcm21664.dtsi
> file remains GPL 2.0 as it originally was.
> 
> make CHECK_DTBS=y on bcm21664-garnet.dtb and bcm23550-sparrow.dtb
> seem to pass fine for me (thanks to Stanislav Jakubek for converting
> the bindings to YAML format!).

:)

> It's worth noting though that some bcm23550 compatibles now go unused,
> since the bcm21664-common.dtsi file uses bcm21664 compatibles.

I don't think this is the way to go. While in these cases the Linux drivers
match only on the generic brcm,kona-* fallback compatible (AFAIK anyway),
the compatibles in DT should still be (SoC-)specific.

I think the common DTSI should omit the compatible values altogether
and instead have the compatible be specified in SoC DTSI. You could keep
a note in the common DTSI saying that the compatible is in SoC DTSI or
something similar.

For example:
- in bcm21664-bcm23550-common.dtsi (or whatever we decide to call it):

gpio: gpio@...300 {
	/* compatible is SoC-specific */
	reg = <0x100300 0x524>;
	...
};

- in bcm21664.dtsi:

&gpio {
	compatible = "brcm,bcm21664-gpio", "brcm,kona-gpio";
};

- in bcm23550.dtsi:

&gpio {
	compatible = "brcm,bcm23550-gpio", "brcm,kona-gpio";
};

Regards,
Stanislav

> 
> [1] https://github.com/knuxdroid/android_kernel_samsung_baffinlite
> 
> Signed-off-by: Artur Weber <aweber.kernel@...il.com>
> ---
> Artur Weber (2):
>       ARM: dts: broadcom: bcm21664: Move chosen node into bcm21664-garnet DTS
>       ARM: dts: bcm-mobile: Split out nodes used by both BCM21664 and BCM23550
> 
>  arch/arm/boot/dts/broadcom/bcm21664-common.dtsi | 334 ++++++++++++++++++++++
>  arch/arm/boot/dts/broadcom/bcm21664-garnet.dts  |   4 +
>  arch/arm/boot/dts/broadcom/bcm21664.dtsi        | 326 +---------------------
>  arch/arm/boot/dts/broadcom/bcm23550.dtsi        | 354 +-----------------------
>  4 files changed, 357 insertions(+), 661 deletions(-)
> ---
> base-commit: a38297e3fb012ddfa7ce0321a7e5a8daeb1872b6
> change-id: 20240528-bcm21664-common-14064864a4a7
> 
> Best regards,
> -- 
> Artur Weber <aweber.kernel@...il.com>
>