[PATCH 10/19] coresight: trbe: Always check fault action when updating buffer

[James Clark]

On 01/12/2025 13:22, Leo Yan wrote:
> The current code checks the fault action only via the IRQ status bit,
> which is unreliable due to possible hardware latency.

This makes it sound like it's fixing a bug, but without a fixes: tag I'm 
assuming it's not a bug. Also I don't get how the change improves the 
latency situation, it still calls trbe_get_fault_act() basically in the 
same place. I think there might be another reason like it makes the code 
cleaner for a later change? Or the commit message needs some elaboration.

> 
> Move the fault action check out of the IRQ status condition.  This also
> causes the buffer size to be calculated for non-WRAP and fault cases,
> which is fine since the write pointer is trusted for the calculation.
> 
> Signed-off-by: Leo Yan <leo.yan at arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-trbe.c | 17 +++--------------
>   1 file changed, 3 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index f56ecdeaa6596afb440e4d53732e08a85f9bf89d..e579ea98523c24d23a0cd265dcdd0a46b52b52da 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -806,7 +806,6 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
>   	enum trbe_fault_action act;
>   	unsigned long size, status;
>   	unsigned long flags;
> -	bool wrap = false;
>   
>   	WARN_ON(buf->cpudata != cpudata);
>   	WARN_ON(cpudata->cpu != smp_processor_id());
> @@ -858,21 +857,11 @@ static unsigned long arm_trbe_update_buffer(struct coresight_device *csdev,
>   		 */
>   		clr_trbe_irq();
>   		isb();
> -
> -		act = trbe_get_fault_act(handle, status);
> -		/*
> -		 * If this was not due to a WRAP event, we have some
> -		 * errors and as such buffer is empty.
> -		 */
> -		if (act != TRBE_FAULT_ACT_WRAP) {
> -			size = 0;
> -			goto done;
> -		}
> -
> -		wrap = true;
>   	}
>   
> -	size = trbe_get_trace_size(handle, buf, wrap);
> +	act = trbe_get_fault_act(handle, status);
> +
> +	size = trbe_get_trace_size(handle, buf, act == TRBE_FAULT_ACT_WRAP);
>   
>   done:
>   	local_irq_restore(flags);
>