Re: [PATCH V2 1/6] coresight: etb10: Properly set AUX buffer head in snapshot mode

[Suzuki K Poulose <suzuki.poulose@arm.com>]

Hi Mathieu,

On 14/05/2019 20:40, Mathieu Poirier wrote:
> Unify amongst sink drivers how the AUX ring buffer head is communicated
> to user space.  That way the same algorithm in cs_etm_find_snapshot()

I would leave the userspace tool's function name out of the commit description
and the comment below. We could instead say: "That way the same algorithm can be
used by the userspace tool to determine the position and the size of the latest
snapshot data."

> can be used to determine where the latest data is and how much of it
> to access.
> 
> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---
>   drivers/hwtracing/coresight/coresight-etb10.c | 13 +++++++------
>   1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etb10.c b/drivers/hwtracing/coresight/coresight-etb10.c
> index 4ee4c80a4354..60e753b1768d 100644
> --- a/drivers/hwtracing/coresight/coresight-etb10.c
> +++ b/drivers/hwtracing/coresight/coresight-etb10.c
> @@ -548,13 +548,14 @@ static unsigned long etb_update_buffer(struct coresight_device *csdev,
>   	writel_relaxed(0x0, drvdata->base + ETB_RAM_WRITE_POINTER);
>   
>   	/*
> -	 * In snapshot mode we have to update the handle->head to point
> -	 * to the new location.
> +	 * In snapshot mode we simply increment the head by the number of byte
> +	 * that were written.  User space function  cs_etm_find_snapshot() will
> +	 * figure out how many bytes to get from the AUX buffer based on the
> +	 * position of the head.
>   	 */
> -	if (buf->snapshot) {
> -		handle->head = (cur * PAGE_SIZE) + offset;
> -		to_read = buf->nr_pages << PAGE_SHIFT;
> -	}
> +	if (buf->snapshot)
> +		handle->head += to_read;
> +
>   	__etb_enable_hw(drvdata);
>   	CS_LOCK(drvdata->base);
>   out:

Otherwise:

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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