linux-kernel - Re: [PATCH v2 RESEND 1/4] coresight: etm4x: Add lock for reading virtual context ID comparator

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Date:   Wed, 9 Feb 2022 09:42:29 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Mike Leach <mike.leach@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 RESEND 1/4] coresight: etm4x: Add lock for reading
 virtual context ID comparator

Hi Leo

On 09/02/2022 09:33, Leo Yan wrote:
> Hi Suzuki,
> 
> On Wed, Feb 09, 2022 at 05:47:24AM +0000, Suzuki Kuruppassery Poulose wrote:
>> Hi Leo
>>
>> On 04/02/2022 15:24, Leo Yan wrote:
>>> Updates to the values and the index are protected via the spinlock.
>>> Ensure we use the same lock to read the value safely.
>>>
>>> Signed-off-by: Leo Yan <leo.yan@...aro.org>
>>> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
>>> ---
>>>    drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
>>> index 10ef2a29006e..2f3b4eef8261 100644
>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
>>> @@ -2111,7 +2111,9 @@ static ssize_t vmid_val_show(struct device *dev,
>>>    	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
>>>    	struct etmv4_config *config = &drvdata->config;
>>> +	spin_lock(&drvdata->spinlock);
>>>    	val = (unsigned long)config->vmid_val[config->vmid_idx];
>>> +	spin_unlock(&drvdata->spinlock);
>>>    	return scnprintf(buf, PAGE_SIZE, "%#lx\n", val);
>>>    }
>>
>>
>> I have queued this patch.
> 
> Thanks!
> 
>> For the rest, we would need to wait until the helper lands in the rc.

Sorry, that was not the exact argument, see below.

> 
> The helper function patch has been landed on the mainline kernel,
> it would be safe to merge the rest patches.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d7e4f8545b497b3f5687e592f1c355cbaee64c8c

The coresight queue is based on rc1 and we already created a stable
tag for TRBE erratas, which was pulled into arm64. So, (correct me
if I am wrong), AFAIU, we cannot rebase the queue on to rc2 where
the patch landed. But happy to proceed, if there is a solution.

Mathieu, what do you think ?

Cheers
Suzuki