Messages in this thread Patch in this message | | | Subject | Re: [PATCH v5 09/15] coresight: trbe: Add infrastructure for Errata handling | From | Anshuman Khandual <> | Date | Tue, 19 Oct 2021 10:55:36 +0530 |
| |
On 10/15/21 4:01 AM, 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. > Thus we will need to check if individual CPUs are affected > by the erratum. > > 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. Though we could reuse the "this_cpu_has_cap()" > to apply an erratum work around, it is a bit of a heavy > operation, as it must go through the "erratum" detection > check on the CPU every time it is called (e.g, scanning > through a table of affected MIDRs). Since we need > to do this check for every session, may be multiple > times (depending on the wrok around), we could save > the cycles by caching the affected errata per-CPU > instance in the per-CPU struct trbe_cpudata. > > Since we are only interested in the errata affecting > the TRBE driver, we only need to track a very few of them > per-CPU. Thus we use a local mapping of the CPUCAP for the > erratum to avoid bloating up a bitmap for trbe_cpudata. > > i.e, each arm64 TRBE erratum bit is assigned a "index" > 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. > > Cc: Mathieu Poirier <mathieu.poirier@linaro.org> > Cc: Mike Leach <mike.leach@linaro.org> > Cc: Leo Yan <leo.yan@linaro.org> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> > --- > Changes since v4: > - Ensure the arm_trbe_probe_cpu() is called from non preemptible > context for hotplugged CPUs
This (both renaming and non preemptible context) makes sense.
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
A small nit though.
Should the array sentinel value '-1' be bit formalized with a macro and check like this != instead.
if (WARN_ON_ONCE(cap != TRBE_ERRATA_SENTINEL))
> Changes since v2: > - Automatically define TRBE_ERRATA_MAX > - Add some basic sanity check to make sure the new entries > are added in order. > - Describe the design choice of caching CPU local errata > in trbe_cpudata instead of using this_cpu_has_cap() > Changes since v1: > - Flip the order of args for trbe_has_erratum() > - Move erratum detection further down in the sequence > --- > drivers/hwtracing/coresight/coresight-trbe.c | 71 +++++++++++++++++++- > 1 file changed, 68 insertions(+), 3 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c > index f8c04c428780..314e5e7374c7 100644 > --- a/drivers/hwtracing/coresight/coresight-trbe.c > +++ b/drivers/hwtracing/coresight/coresight-trbe.c > @@ -16,6 +16,7 @@ > #define pr_fmt(fmt) DRVNAME ": " fmt > > #include <asm/barrier.h> > + > #include "coresight-self-hosted-trace.h" > #include "coresight-trbe.h" > > @@ -67,14 +68,43 @@ struct trbe_buf { > struct trbe_cpudata *cpudata; > }; > > +/* > + * TRBE erratum list > + * > + * The errata are defined in arm64 generic cpu_errata framework. > + * Since the errata work arounds could be applied individually > + * to the affected CPUs inside the TRBE driver, we need to know if > + * a given CPU is affected by the erratum. Unlike the other erratum > + * work arounds, TRBE driver needs to check multiple times during > + * a trace session. Thus we need a quicker access to per-CPU > + * errata and not issue costly this_cpu_has_cap() everytime. > + * We keep a set of the affected errata in trbe_cpudata, per TRBE. > + * > + * 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 > + */ > + > +static int trbe_errata_cpucaps[] = { > + -1, /* Sentinel, must be the last entry */ > +}; > + > +/* The total number of listed errata in trbe_errata_cpucaps */ > +#define TRBE_ERRATA_MAX (ARRAY_SIZE(trbe_errata_cpucaps) - 1) > + > /* > * struct trbe_cpudata: TRBE instance specific data > * @trbe_flag - TRBE dirty/access flag support > * @trbe_hw_align - Actual TRBE alignment required for TRBPTR_EL1. > - * @trbe_align - Software alignment used for the TRBPTR_EL1, > + * @trbe_align - Software alignment used for the 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; > @@ -84,6 +114,7 @@ struct trbe_cpudata { > enum cs_mode mode; > struct trbe_buf *buf; > struct trbe_drvdata *drvdata; > + DECLARE_BITMAP(errata, TRBE_ERRATA_MAX); > }; > > struct trbe_drvdata { > @@ -96,6 +127,25 @@ struct trbe_drvdata { > struct platform_device *pdev; > }; > > +static void trbe_check_errata(struct trbe_cpudata *cpudata) > +{ > + int i; > + > + for (i = 0; i < TRBE_ERRATA_MAX; i++) { > + int cap = trbe_errata_cpucaps[i]; > + > + if (WARN_ON_ONCE(cap < 0)) > + return; > + if (this_cpu_has_cap(cap)) > + set_bit(i, cpudata->errata); > + } > +} > + > +static inline bool trbe_has_erratum(struct trbe_cpudata *cpudata, int i) > +{ > + return (i < TRBE_ERRATA_MAX) && test_bit(i, cpudata->errata); > +} > + > static int trbe_alloc_node(struct perf_event *event) > { > if (event->cpu == -1) > @@ -952,6 +1002,9 @@ static void arm_trbe_register_coresight_cpu(struct trbe_drvdata *drvdata, int cp > cpumask_clear_cpu(cpu, &drvdata->supported_cpus); > } > > +/* > + * Must be called with preemption disabled, for trbe_check_errata(). > + */ > static void arm_trbe_probe_cpu(void *info) > { > struct trbe_drvdata *drvdata = info; > @@ -979,6 +1032,12 @@ static void arm_trbe_probe_cpu(void *info) > goto cpu_clear; > } > > + /* > + * Run the TRBE erratum checks, now that we know > + * this instance is about to be registered. > + */ > + trbe_check_errata(cpudata); > + > cpudata->trbe_align = cpudata->trbe_hw_align; > cpudata->trbe_flag = get_trbe_flag_update(trbidr); > cpudata->cpu = cpu; > @@ -1032,18 +1091,24 @@ static int arm_trbe_remove_coresight(struct trbe_drvdata *drvdata) > return 0; > } > > +static void arm_trbe_probe_hotplugged_cpu(struct trbe_drvdata *drvdata) > +{ > + preempt_disable(); > + arm_trbe_probe_cpu(drvdata); > + preempt_enable(); > +} > + > static int arm_trbe_cpu_startup(unsigned int cpu, struct hlist_node *node) > { > struct trbe_drvdata *drvdata = hlist_entry_safe(node, struct trbe_drvdata, hotplug_node); > > if (cpumask_test_cpu(cpu, &drvdata->supported_cpus)) { > - > /* > * If this CPU was not probed for TRBE, > * initialize it now. > */ > if (!coresight_get_percpu_sink(cpu)) { > - arm_trbe_probe_cpu(drvdata); > + arm_trbe_probe_hotplugged_cpu(drvdata); > if (cpumask_test_cpu(cpu, &drvdata->supported_cpus)) > arm_trbe_register_coresight_cpu(drvdata, cpu); > if (cpumask_test_cpu(cpu, &drvdata->supported_cpus)) >
| |