Re: [PATCH 01/10] coresight: trbe: Add infrastructure for Errata handling

From: Anshuman Khandual
Date: Mon Aug 02 2021 - 02:43:06 EST




On 7/28/21 7:22 PM, Suzuki K Poulose wrote:
> Add a minimal infrastructure to keep track of the errata
> affecting the given TRBE instance. Given that we have
> heterogeneous CPUs, we have to manage the list per-TRBE
> instance to be able to apply the work around as needed.
>
> We rely on the arm64 errata framework for the actual
> description and the discovery of a given erratum, to
> keep the Erratum work around at a central place and
> benefit from the code and the advertisement from the
> kernel. We use a local mapping of the erratum to
> avoid bloating up the individual TRBE structures.

I guess there is no other way around apart from each TRBE instance
tracking applicable erratas locally per CPU, even though it sounds
bit redundant.

> i.e, each arm64 TRBE erratum bit is assigned a new number
> within the driver to track. Each trbe instance updates
> the list of affected erratum at probe time on the CPU.
> This makes sure that we can easily access the list of
> errata on a given TRBE instance without much overhead.

It also ensures that the generic errata framework is queried just
once during individual CPU probe.

>
> Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
> drivers/hwtracing/coresight/coresight-trbe.c | 48 ++++++++++++++++++++
> 1 file changed, 48 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index b8586c170889..0368bf405e35 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -16,6 +16,8 @@
> #define pr_fmt(fmt) DRVNAME ": " fmt
>
> #include <asm/barrier.h>
> +#include <asm/cputype.h>
> +
> #include "coresight-self-hosted-trace.h"
> #include "coresight-trbe.h"
>
> @@ -65,6 +67,35 @@ struct trbe_buf {
> struct trbe_cpudata *cpudata;
> };
>
> +/*
> + * TRBE erratum list
> + *
> + * We rely on the corresponding cpucaps to be defined for a given
> + * TRBE erratum. We map the given cpucap into a TRBE internal number
> + * to make the tracking of the errata lean.
> + *
> + * This helps in :
> + * - Not duplicating the detection logic
> + * - Streamlined detection of erratum across the system
> + *
> + * Since the erratum work arounds could be applied individually
> + * per TRBE instance, we keep track of the list of errata that
> + * affects the given instance of the TRBE.
> + */
> +#define TRBE_ERRATA_MAX 0
> +
> +static unsigned long trbe_errata_cpucaps[TRBE_ERRATA_MAX] = {
> +};

This needs to be tighten up. There should be build time guard rails in
arm64 errata cpucaps, so that only TRBE specific ones could be assigned
here as trbe_errata_cpucaps[].

> +
> +/*
> + * struct trbe_cpudata: TRBE instance specific data
> + * @trbe_flag - TRBE dirty/access flag support
> + * @tbre_align - Actual TRBE alignment required for TRBPTR_EL1.
> + * @cpu - CPU this TRBE belongs to.
> + * @mode - Mode of current operation. (perf/disabled)
> + * @drvdata - TRBE specific drvdata
> + * @errata - Bit map for the errata on this TRBE.
> + */
> struct trbe_cpudata {
> bool trbe_flag;
> u64 trbe_align;
> @@ -72,6 +103,7 @@ struct trbe_cpudata {
> enum cs_mode mode;
> struct trbe_buf *buf;
> struct trbe_drvdata *drvdata;
> + DECLARE_BITMAP(errata, TRBE_ERRATA_MAX);
> };
>
> struct trbe_drvdata {
> @@ -84,6 +116,21 @@ struct trbe_drvdata {
> struct platform_device *pdev;
> };
>
> +static void trbe_check_errata(struct trbe_cpudata *cpudata)
> +{
> + int i;
> +
> + for (i = 0; i < ARRAY_SIZE(trbe_errata_cpucaps); i++) {

BUILD_BUG_ON() - if trbe_errata_cpucaps[i] is not inside TRBE specific
errata cpucap range ?

> + if (this_cpu_has_cap(trbe_errata_cpucaps[i]))
> + set_bit(i, cpudata->errata);
> + }
> +}
> +
> +static inline bool trbe_has_erratum(int i, struct trbe_cpudata *cpudata)

Switch the argument positions here ? 'int i' should be the second one.

> +{
> + return (i < TRBE_ERRATA_MAX) && test_bit(i, cpudata->errata);
> +}
> +
> static int trbe_alloc_node(struct perf_event *event)
> {
> if (event->cpu == -1)
> @@ -925,6 +972,7 @@ static void arm_trbe_probe_cpu(void *info)
> goto cpu_clear;
> }
>
> + trbe_check_errata(cpudata);

This should be called right at the end before arm_trbe_probe_cpu() exits
on the success path. Errata should not be evaluated if TRBE on the CPU
wont be used for some reason i.e cpumask_clear_cpu() path.

> cpudata->trbe_align = 1ULL << get_trbe_address_align(trbidr);
> if (cpudata->trbe_align > SZ_2K) {
> pr_err("Unsupported alignment on cpu %d\n", cpu);
>

This patch should be moved after [PATCH 5/10] i.e just before adding the
first TRBE errata.