Re: [PATCH 3/3] arm64: perf: Support new DT compatibles

[Andre Przywara <andre.przywara@arm.com>]

On Fri, 21 Feb 2020 16:04:58 +0000
Robin Murphy <robin.murphy@arm.com> wrote:

Hi,

> Add support for matching the new PMUs. For now, this just wires them up
> as generic PMUv3 such that people writing DTs for new SoCs can do the
> right thing, and at least have architectural and raw events be usable.
> We can come back and fill in event maps for sysfs and/or perf tools at
> a later date.

as mentioned already in a reply to another patch:

Is that really the right way? Isn't that calling for the intended usage of a compatible fall-back string?
So that a machine can just ship DTBs with for instance:
	"arm,neoverse-n1-pmu", "arm,armv8-pmuv3";
and that would magically work with all older and newer kernels already, without any patch?

As it stands right now (with a single compatible), only newer kernels could use the PMU on those SoCs (ignoring tedious backports not reaching every user).

All that would be needed for that is to officially allow two compatible strings in the binding.

Cheers,
Andre.

P.S. Still thinking about dropping those compatible strings at all and using the MIDR somehow, because then also ACPI users would benefit from core specific events.
 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  arch/arm64/kernel/perf_event.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index e40b65645c86..28ce582e049e 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -1105,11 +1105,19 @@ static int armv8_vulcan_pmu_init(struct arm_pmu *cpu_pmu)
>  
>  static const struct of_device_id armv8_pmu_of_device_ids[] = {
>  	{.compatible = "arm,armv8-pmuv3",	.data = armv8_pmuv3_init},
> +	{.compatible = "arm,cortex-a34-pmu",	.data = armv8_pmuv3_init},
>  	{.compatible = "arm,cortex-a35-pmu",	.data = armv8_a35_pmu_init},
>  	{.compatible = "arm,cortex-a53-pmu",	.data = armv8_a53_pmu_init},
> +	{.compatible = "arm,cortex-a55-pmu",	.data = armv8_pmuv3_init},
>  	{.compatible = "arm,cortex-a57-pmu",	.data = armv8_a57_pmu_init},
> +	{.compatible = "arm,cortex-a65-pmu",	.data = armv8_pmuv3_init},
>  	{.compatible = "arm,cortex-a72-pmu",	.data = armv8_a72_pmu_init},
>  	{.compatible = "arm,cortex-a73-pmu",	.data = armv8_a73_pmu_init},
> +	{.compatible = "arm,cortex-a75-pmu",	.data = armv8_pmuv3_init},
> +	{.compatible = "arm,cortex-a76-pmu",	.data = armv8_pmuv3_init},
> +	{.compatible = "arm,cortex-a77-pmu",	.data = armv8_pmuv3_init},
> +	{.compatible = "arm,neoverse-e1-pmu",	.data = armv8_pmuv3_init},
> +	{.compatible = "arm,neoverse-n1-pmu",	.data = armv8_pmuv3_init},
>  	{.compatible = "cavium,thunder-pmu",	.data = armv8_thunder_pmu_init},
>  	{.compatible = "brcm,vulcan-pmu",	.data = armv8_vulcan_pmu_init},
>  	{},