linux-kernel - Re: [PATCH 04/10] coresight: trbe: Decouple buffer base from the hardware base

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Date:   Fri, 30 Jul 2021 16:23:09 +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, coresight@...ts.linaro.org,
        will@...nel.org, catalin.marinas@....com, james.morse@....com,
        mathieu.poirier@...aro.org, mike.leach@...aro.org,
        leo.yan@...aro.org, maz@...nel.org, mark.rutland@....com
Subject: Re: [PATCH 04/10] coresight: trbe: Decouple buffer base from the
 hardware base



On 7/28/21 7:22 PM, Suzuki K Poulose wrote:
> We always set the TRBBASER_EL1 to the base of the virtual ring
> buffer. We are about to change this for working around an erratum.
> So, in preparation to that, allow the driver to choose a different
> base for the TRBBASER_EL1 (which is within the buffer range).
> 
> 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 | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 0af644331b99..9735d514c5e1 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -59,6 +59,8 @@ struct trbe_buf {
>  	 * trbe_limit sibling pointers.
>  	 */
>  	unsigned long trbe_base;
> +	/* The base programmed into the TRBE */
> +	unsigned long trbe_hw_base;
>  	unsigned long trbe_limit;
>  	unsigned long trbe_write;
>  	int nr_pages;
> @@ -504,7 +506,7 @@ static void trbe_enable_hw(struct trbe_buf *buf)
>  	set_trbe_disabled();
>  	isb();
>  	clr_trbe_status();
> -	set_trbe_base_pointer(buf->trbe_base);
> +	set_trbe_base_pointer(buf->trbe_hw_base);

It might be better to add a sanity check asserting 'buf->trbe_hw_base' to
be within [buf->trbe_base..buf->trbe_base + nr_pages * PAGE_SIZE] before
writing that into TRBBASER_EL1.

>  	set_trbe_write_pointer(buf->trbe_write);
>  
>  	/*
> @@ -709,6 +711,8 @@ static int __arm_trbe_enable(struct trbe_buf *buf,
>  		trbe_stop_and_truncate_event(handle);
>  		return -ENOSPC;
>  	}
> +	/* Set the base of the TRBE to the buffer base */
> +	buf->trbe_hw_base = buf->trbe_base;

So applicable 'buf->trbe_hw_base' will be derived from 'buf->trbe_base'
after taking into account workarounds (if any). Makes sense.

>  	*this_cpu_ptr(buf->cpudata->drvdata->handle) = handle;
>  	trbe_enable_hw(buf);
>  	return 0;
> @@ -808,7 +812,7 @@ static bool is_perf_trbe(struct perf_output_handle *handle)
>  	struct trbe_drvdata *drvdata = cpudata->drvdata;
>  	int cpu = smp_processor_id();
>  
> -	WARN_ON(buf->trbe_base != get_trbe_base_pointer());
> +	WARN_ON(buf->trbe_hw_base != get_trbe_base_pointer());
>  	WARN_ON(buf->trbe_limit != get_trbe_limit_pointer());
>  
>  	if (cpudata->mode != CS_MODE_PERF)
> 

With or without the above sanity check.

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