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 for <linuxppc-dev@lists.ozlabs.org> from <vaibhav@linux.vnet.ibm.com>;
 Sun, 11 Feb 2018 17:10:28 -0000
From: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
To: christophe lombard <clombard@linux.vnet.ibm.com>,
 linuxppc-dev@lists.ozlabs.org, Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Cc: Philippe Bergheaud <philippe.bergheaud@fr.ibm.com>,
 "Alastair D'Silva" <alastair@linux.ibm.com>,
 Christophe Lombard <christophe_lombard@fr.ibm.com>,
 Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Subject: Re: [PATCH 2/3] cxl: Introduce module parameter 'enable_psltrace'
In-Reply-To: <a3880a5d-6ccb-9a90-14e5-d48376e4c8e0@linux.vnet.ibm.com>
References: <20180209042535.16845-1-vaibhav@linux.vnet.ibm.com>
 <20180209042535.16845-3-vaibhav@linux.vnet.ibm.com>
 <a3880a5d-6ccb-9a90-14e5-d48376e4c8e0@linux.vnet.ibm.com>
Date: Sun, 11 Feb 2018 22:40:18 +0530
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Thanks for reviewing the patch Christophe,

christophe lombard <clombard@linux.vnet.ibm.com> writes:
>> +bool cxl_enable_psltrace = true;
>> +module_param_named(enable_psltrace, cxl_enable_psltrace, bool, 0600);
>> +MODULE_PARM_DESC(enable_psltrace, "Set PSL traces on probe. default: on");
>> +
> I am not too agree to add a new parameter. This can cause doubts.
> PSL team has confirmed that enabling traces has no impact.
> Do you see any reason to disable the traces ?

Traces on PSL follow a 'set and fetch' model. So once the trace buffer for
a specific array is full it will stop and switch to 'FIN' state and at
that point we need to fetch the trace-data and reinit the array to
re-arm it.

There might be some circumstances where this model may lead to confusion
specifically when AFU developers assume that the trace arrays are
already armed and dont re-arm it causing miss of trace data.

So this module param is a compromise to keep the old behaviour of traces
array intact where in the arming/disarming of the trace arrays is
controlled completely by userspace tooling and not by cxl.

-- 
Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.