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SubjectRe: [PATCH v2 03/17] coresight: trbe: Add a helper to calculate the trace generated
Hi Suzuki,

On Tue, Sep 21, 2021 at 02:41:07PM +0100, Suzuki K Poulose wrote:
> We collect the trace from the TRBE on FILL event from IRQ context
> and when via update_buffer(), when the event is stopped. Let us

s/"and when via"/"and via"

> consolidate how we calculate the trace generated into a helper.
>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> drivers/hwtracing/coresight/coresight-trbe.c | 48 ++++++++++++--------
> 1 file changed, 30 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 63f7edd5fd1f..063c4505a203 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -527,6 +527,30 @@ static enum trbe_fault_action trbe_get_fault_act(u64 trbsr)
> return TRBE_FAULT_ACT_SPURIOUS;
> }
>
> +static unsigned long trbe_get_trace_size(struct perf_output_handle *handle,
> + struct trbe_buf *buf,
> + bool wrap)

Stacking

> +{
> + u64 write;
> + u64 start_off, end_off;
> +
> + /*
> + * If the TRBE has wrapped around the write pointer has
> + * wrapped and should be treated as limit.
> + */
> + if (wrap)
> + write = get_trbe_limit_pointer();
> + else
> + write = get_trbe_write_pointer();
> +
> + end_off = write - buf->trbe_base;

In both arm_trbe_alloc_buffer() and trbe_handle_overflow() the base address is
acquired using get_trbe_base_pointer() but here it is referenced directly - any
reason for that? It certainly makes reviewing this simple patch quite
difficult because I keep wondering if I am missing something subtle...

> + start_off = PERF_IDX2OFF(handle->head, buf);
> +
> + if (WARN_ON_ONCE(end_off < start_off))
> + return 0;
> + return (end_off - start_off);
> +}
> +
> static void *arm_trbe_alloc_buffer(struct coresight_device *csdev,
> struct perf_event *event, void **pages,
> int nr_pages, bool snapshot)
> @@ -588,9 +612,9 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
> struct trbe_cpudata *cpudata = dev_get_drvdata(&csdev->dev);
> struct trbe_buf *buf = config;
> enum trbe_fault_action act;
> - unsigned long size, offset;
> - unsigned long write, base, status;
> + unsigned long size, status;
> unsigned long flags;
> + bool wrap = false;
>
> WARN_ON(buf->cpudata != cpudata);
> WARN_ON(cpudata->cpu != smp_processor_id());
> @@ -630,8 +654,6 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
> * handle gets freed in etm_event_stop().
> */
> trbe_drain_and_disable_local();
> - write = get_trbe_write_pointer();
> - base = get_trbe_base_pointer();
>
> /* Check if there is a pending interrupt and handle it here */
> status = read_sysreg_s(SYS_TRBSR_EL1);
> @@ -655,20 +677,11 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
> goto done;
> }
>
> - /*
> - * Otherwise, the buffer is full and the write pointer
> - * has reached base. Adjust this back to the Limit pointer
> - * for correct size. Also, mark the buffer truncated.
> - */
> - write = get_trbe_limit_pointer();
> perf_aux_output_flag(handle, PERF_AUX_FLAG_COLLISION);
> + wrap = true;
> }
>
> - offset = write - base;
> - if (WARN_ON_ONCE(offset < PERF_IDX2OFF(handle->head, buf)))
> - size = 0;
> - else
> - size = offset - PERF_IDX2OFF(handle->head, buf);
> + size = trbe_get_trace_size(handle, buf, wrap);
>
> done:
> local_irq_restore(flags);
> @@ -749,11 +762,10 @@ static int trbe_handle_overflow(struct perf_output_handle *handle)
> {
> struct perf_event *event = handle->event;
> struct trbe_buf *buf = etm_perf_sink_config(handle);
> - unsigned long offset, size;
> + unsigned long size;
> struct etm_event_data *event_data;
>
> - offset = get_trbe_limit_pointer() - get_trbe_base_pointer();
> - size = offset - PERF_IDX2OFF(handle->head, buf);
> + size = trbe_get_trace_size(handle, buf, true);
> if (buf->snapshot)
> handle->head += size;
>
> --
> 2.24.1
>

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