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 for <linuxppc-dev@lists.ozlabs.org> from <clombard@linux.vnet.ibm.com>;
 Mon, 12 Feb 2018 10:46:24 -0000
Subject: Re: [PATCH 2/3] cxl: Introduce module parameter 'enable_psltrace'
To: Vaibhav Jain <vaibhav@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>
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>
 <87a7wf4flx.fsf@vajain21.in.ibm.com>
From: christophe lombard <clombard@linux.vnet.ibm.com>
Date: Mon, 12 Feb 2018 11:46:21 +0100
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Le 11/02/2018 à 18:10, Vaibhav Jain a écrit :
> 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.
> 
and about P8 ? This new parameter is only useful for P9. It will be 
confusing.