Re: [PATCH v13 2/3] perf: Add Raspberry Pi BCM2835 AXI PMU driver

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Inclusion of LINUX_VERSION_CODE checks for out-of-tree/LTS compatibility in mainline code.
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--- Patch [2]: [PATCH v13 2/3] perf: Add Raspberry Pi BCM2835 AXI PMU driver ---
commit c667a74c49bf6e5e64002019c6914cc36bf088da
Author: Ian Rogers <irogers@google.com>
perf: Add Raspberry Pi BCM2835 AXI PMU driver

This commit adds a new performance monitoring driver for the Raspberry Pi
AXI bus (BCM2835/2711), exposing system-level and VideoCore PMU hardware to
the Linux perf subsystem natively via the VideoCore mailbox interface.

> Note on out-of-tree macro compatibility:
> The inclusion of #if LINUX_VERSION_CODE < KERNEL_VERSION(6, 13, 0)
> surrounding hrtimer_setup is intentionally maintained alongside
> this patch to guarantee seamless out-of-tree compilation fallback
> compatibility for Raspberry Pi Long Term Support (LTS) kernel variants.

[Severity: Low]
This isn't a bug, but does upstream accept LINUX_VERSION_CODE macros for
backward compatibility in mainline code? Upstream policy generally prohibits
adding backward compatibility ifdefs to support out-of-tree or older LTS
kernels. All code submitted to mainline is expected to compile against the
current kernel's internal API, leaving backward compatibility to stable tree
backporters or out-of-tree maintainers.

> diff --git a/drivers/perf/rpi_axi_pmu.c b/drivers/perf/rpi_axi_pmu.c
> new file mode 100644
> --- /dev/null
> +++ b/drivers/perf/rpi_axi_pmu.c
[ ... ]
> +#include <linux/io.h>
> +#include <linux/version.h>
> +
> +#if LINUX_VERSION_CODE < KERNEL_VERSION(6, 13, 0)
> +static inline void rpi_hrtimer_setup(struct hrtimer *timer,
> +				     enum hrtimer_restart (*function)(struct hrtimer *),
> +				     clockid_t clock_id, enum hrtimer_mode mode)
> +{
> +	hrtimer_init(timer, clock_id, mode);
> +	timer->function = function;
> +}
> +#define hrtimer_setup rpi_hrtimer_setup
> +#endif

[Severity: Low]
Can we remove rpi_hrtimer_setup() and the LINUX_VERSION_CODE check from
drivers/perf/rpi_axi_pmu.c? As mentioned above, maintaining out-of-tree
compatibility macros adds unnecessary code complexity to the mainline kernel.

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Sashiko AI review · https://sashiko.dev/#/patchset/20260815172712.50119-1-irogers@google.com?part=2