linux-kernel - Re: [PATCH v2 13/17] coresight: trbe: Add a helper to determine the minimum buffer size

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Date:   Wed, 22 Sep 2021 15:21:49 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, maz@...nel.org,
        catalin.marinas@....com, mark.rutland@....com, james.morse@....com,
        leo.yan@...aro.org, mike.leach@...aro.org,
        mathieu.poirier@...aro.org, will@...nel.org, lcherian@...vell.com,
        coresight@...ts.linaro.org
Subject: Re: [PATCH v2 13/17] coresight: trbe: Add a helper to determine the
 minimum buffer size



On 9/21/21 7:11 PM, Suzuki K Poulose wrote:
> For the TRBE to operate, we need a minimum space available to collect
> meaningful trace session. This is currently a few bytes, but we may need
> to extend this for working around errata. So, abstract this into a helper
> function.
> 
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 797d978f9fa7..3373f4e2183b 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -277,6 +277,11 @@ trbe_handle_to_cpudata(struct perf_output_handle *handle)
>  	return buf->cpudata;
>  }
>  
> +static u64 trbe_min_trace_buf_size(struct perf_output_handle *handle)
> +{
> +	return TRBE_TRACE_MIN_BUF_SIZE;
> +}

Assuming that struct perf_output_handle could provide all the
required support for a variable minimum trace buffer length.

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>

> +
>  /*
>   * TRBE Limit Calculation
>   *
> @@ -447,7 +452,7 @@ static unsigned long trbe_normal_offset(struct perf_output_handle *handle)
>  	 * have space for a meaningful run, we rather pad it
>  	 * and start fresh.
>  	 */
> -	if (limit && (limit - head < TRBE_TRACE_MIN_BUF_SIZE)) {
> +	if (limit && ((limit - head) < trbe_min_trace_buf_size(handle))) {
>  		trbe_pad_buf(handle, limit - head);
>  		limit = __trbe_normal_offset(handle);
>  	}
>