Re: [Xen-devel] [PATCH] xen/arm: platform: additional Raspberry Pi compatible string

[Stewart Hildebrand <Stewart.Hildebrand@xxxxxxxxxxxxxxx>]

On Friday, September 13, 2019 5:42 PM, Julien Grall <julien.grall@xxxxxxx> 
wrote:
>Hi,
>
>On 9/13/19 8:11 PM, Stewart Hildebrand wrote:
>> Upstream Linux kernel will use "brcm,bcm2711" as the compatible string
>> for Raspberry Pi 4 [1]. Add this string to our platform compatible list
>> for compatibility with the upstream kernel.
>
>This raises a few questions:
>    1) Why such discrepancies in naming?

Traditionally the raspberry pi tree has used the bcm2708/9/10 naming 
convention, and upstream bcm2835/6/7. It seems they've switched it up for the 
RPi4. In the RFC version of the series intended for upstream, they indeed had 
it as 2838 [2], but after that it changed to 2711 [3] [4].

The SoC name in documentation is BCM2711 [5] [6].

>    2) Is the patch [1] merged? If so, which version?

No.

>    3) Both upstream and non-upstream seem to have the compatible
>"raspberrypi,4-model-b", so would it make sense to check that instead?

"raspberrypi,4-model-b" describes a board, and "brcm,bcm2xxx" describes a SoC. 
It is feasible that there will be more boards based on this SoC, in which case 
we'd have to add those hypothetical new boards separately. If we list both 
"brcm,bcm2711" and "brcm,bcm2838", then it seems to me we'd have a better 
chance at matching future boards with this particular SoC, while also matching 
both upstream and non-upstream trees.

>>   static const char *const brcm_bcm2838_dt_compat[] __initconst =
>>   {
>> +    "brcm,bcm2711",
>
>If a new compatible is added, then you likely need to rename the
>different structure within this file.

Good point. Since the documentation uses the BCM2711 convention, it would make 
sense to me to rename it reflecting this, even when the list contains both 
brcm,bcm2711 and brcm,bcm2838. And perhaps also add a comment by the 
brcm,bcm2838 entry to explain the oddity.

static const char *const brcm_bcm2711_dt_compat[] __initconst =
{
    "brcm,bcm2711",
    /*
     * While the name of the SoC is BCM2711, some variants of Linux
     * have also used the brcm,bcm2838 naming convention. We consider
     * either compatible string to be a valid match for the BCM2711 SoC.
     */
    "brcm,bcm2838",

The bcm2838 naming convention statement ironically refers to the raspberry pi 
tree [7].

[2] RFC https://patchwork.kernel.org/cover/11048215/#22767107
[3] v1 https://patchwork.kernel.org/cover/11051653/
[4] v2 https://patchwork.kernel.org/cover/11092641/
[5] 
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711/README.md
[6] 
https://www.raspberrypi.org/documentation/hardware/raspberrypi/bcm2711/rpi_DATA_2711_1p0_preliminary.pdf
[7] 
https://github.com/raspberrypi/linux/blob/rpi-4.19.y/arch/arm/boot/dts/bcm2711-rpi-4-b.dts#L8
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