linux-kernel - Re: [PATCH v3 19/26] coresight: etm4x: Detect access early on the target CPU

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Message-ID: <f66695c0-e436-0d5c-2e12-5383159e72d6@arm.com>
Date:   Mon, 9 Nov 2020 09:48:07 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, mike.leach@...aro.org,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 19/26] coresight: etm4x: Detect access early on the
 target CPU

On 11/6/20 8:34 PM, Mathieu Poirier wrote:
> On Wed, Oct 28, 2020 at 10:09:38PM +0000, Suzuki K Poulose wrote:
>> In preparation to detect the support for system instruction
>> support, move the detection of the device access to the target
>> CPU.
>>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>   .../coresight/coresight-etm4x-core.c          | 45 ++++++++++++++++---
>>   1 file changed, 40 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> index f038bb10bc78..308674ab746c 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> @@ -56,6 +56,11 @@ static u64 etm4_get_access_type(struct etmv4_config *config);
>>   
>>   static enum cpuhp_state hp_online;
>>   
>> +struct etm_init_arg {
> 
> s/etm_init_arg/etm4_init_arg

Part of the reason was to add a future IP support where it is not all
ETM4. Again it doesn't really matter. I could change it.

> 
>> +	struct etmv4_drvdata	*drvdata;
>> +	struct csdev_access	*csa;
>> +};
>> +
>>   u64 etm4x_sysreg_read(struct csdev_access *csa,
>>   		      u32 offset,
>>   		      bool _relaxed,
>> @@ -669,6 +674,22 @@ static const struct coresight_ops etm4_cs_ops = {
>>   	.source_ops	= &etm4_source_ops,
>>   };
>>   
>> +static bool etm_init_iomem_access(struct etmv4_drvdata *drvdata,
>> +				  struct csdev_access *csa)
>> +{
>> +	*csa = CSDEV_ACCESS_IOMEM(drvdata->base);
>> +	return true;
>> +}
>> +
>> +static bool etm_init_csdev_access(struct etmv4_drvdata *drvdata,
>> +				  struct csdev_access *csa)
>> +{
>> +	if (drvdata->base)
>> +		return etm_init_iomem_access(drvdata, csa);
>> +
>> +	return false;
>> +}
> 
> Returning a boolean rather than an int for the above two functions seems odd to
> me.
> 

We don't return an error from the caller of these functions. So, all we
need to know is, if the operation was success or failure. Having bool
makes it explicit for the checkings, rather than documenting the
expected return values. Hence the choice. But I am open to changing them
if you prefer it that way.



Cheers
Suzuki