linux-kernel - Re: [PATCH 05/10] coresight: trbe: Allow driver to choose a different alignment

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Message-ID: <646d73c5-0015-d296-2ac8-63f8bd5a4dc0@arm.com>
Date:   Fri, 30 Jul 2021 16:32:54 +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 05/10] coresight: trbe: Allow driver to choose a different
 alignment



On 7/28/21 7:22 PM, Suzuki K Poulose wrote:
> The TRBE hardware mandates a minimum alignment for the TRBPTR_EL1,
> advertised via the TRBIDR_EL1. This is used by the driver to
> align the buffer write head. This patch allows the driver to
> choose a different alignment from that of the hardware, by
> decoupling the alignment tracking. This will be useful for
> working around errata.
> 
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  drivers/hwtracing/coresight/coresight-trbe.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
> index 9735d514c5e1..9ea28813182b 100644
> --- a/drivers/hwtracing/coresight/coresight-trbe.c
> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
> @@ -92,7 +92,8 @@ static unsigned long trbe_errata_cpucaps[TRBE_ERRATA_MAX] = {
>  /*
>   * struct trbe_cpudata: TRBE instance specific data
>   * @trbe_flag		- TRBE dirty/access flag support
> - * @tbre_align		- Actual TRBE alignment required for TRBPTR_EL1.
> + * @trbe_hw_align	- Actual TRBE alignment required for TRBPTR_EL1.
> + * @trbe_align		- Software alignment used for the TRBPTR_EL1,
>   * @cpu			- CPU this TRBE belongs to.
>   * @mode		- Mode of current operation. (perf/disabled)
>   * @drvdata		- TRBE specific drvdata
> @@ -100,6 +101,7 @@ static unsigned long trbe_errata_cpucaps[TRBE_ERRATA_MAX] = {
>   */
>  struct trbe_cpudata {
>  	bool trbe_flag;
> +	u64 trbe_hw_align;
>  	u64 trbe_align;
>  	int cpu;
>  	enum cs_mode mode;
> @@ -906,7 +908,7 @@ static ssize_t align_show(struct device *dev, struct device_attribute *attr, cha
>  {
>  	struct trbe_cpudata *cpudata = dev_get_drvdata(dev);
>  
> -	return sprintf(buf, "%llx\n", cpudata->trbe_align);
> +	return sprintf(buf, "%llx\n", cpudata->trbe_hw_align);
>  }
>  static DEVICE_ATTR_RO(align);
>  
> @@ -995,11 +997,13 @@ static void arm_trbe_probe_cpu(void *info)
>  	}
>  
>  	trbe_check_errata(cpudata);
> -	cpudata->trbe_align = 1ULL << get_trbe_address_align(trbidr);
> -	if (cpudata->trbe_align > SZ_2K) {
> +
> +	cpudata->trbe_hw_align = 1ULL << get_trbe_address_align(trbidr);
> +	if (cpudata->trbe_hw_align > SZ_2K) {
>  		pr_err("Unsupported alignment on cpu %d\n", cpu);
>  		goto cpu_clear;
>  	}
> +	cpudata->trbe_align = cpudata->trbe_hw_align;

When it changes, it must be asserted that trbe_align would be a multiple
of trbe_hw_align before existing from arm_trbe_probe_cpu().

>  	cpudata->trbe_flag = get_trbe_flag_update(trbidr);
>  	cpudata->cpu = cpu;
>  	cpudata->drvdata = drvdata;
> 

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