linux-kernel - Re: [PATCH v6 03/11] powerpc/powernv: Detect supported IMC units and its events

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Date:   Mon, 17 Apr 2017 13:38:10 +0530
From:   Anju T Sudhakar <anju@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Stewart Smith <stewart@...ux.vnet.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ego@...ux.vnet.ibm.com, bsingharora@...il.com,
        benh@...nel.crashing.org, paulus@...ba.org, anton@...ba.org,
        sukadev@...ux.vnet.ibm.com, mikey@...ling.org, dja@...ens.net,
        eranian@...gle.com, Hemant Kumar <hemant@...ux.vnet.ibm.com>
Subject: Re: [PATCH v6 03/11] powerpc/powernv: Detect supported IMC units and
 its events

Hi Michael,


On Thursday 13 April 2017 05:13 PM, Michael Ellerman wrote:
> Anju T Sudhakar <anju@...ux.vnet.ibm.com> writes:
>> On Thursday 06 April 2017 02:07 PM, Stewart Smith wrote:
>>> Madhavan Srinivasan <maddy@...ux.vnet.ibm.com> writes:
>>>> --- a/arch/powerpc/platforms/powernv/opal-imc.c
>>>> +++ b/arch/powerpc/platforms/powernv/opal-imc.c
>>>> @@ -33,6 +33,388 @@
>>> <snip>
>>>> +static void imc_pmu_setup(struct device_node *parent)
>>>> +{
>>>> +	struct device_node *child;
>>>> +	int pmu_count = 0, rc = 0;
>>>> +	const struct property *pp;
>>>> +
>>>> +	if (!parent)
>>>> +		return;
>>>> +
>>>> +	/* Setup all the IMC pmus */
>>>> +	for_each_child_of_node(parent, child) {
>>>> +		pp = of_get_property(child, "compatible", NULL);
>>>> +		if (pp) {
>>>> +			/*
>>>> +			 * If there is a node with a "compatible" field,
>>>> +			 * that's a PMU node
>>>> +			 */
>>>> +			rc = imc_pmu_create(child, pmu_count);
>>>> +			if (rc)
>>>> +				return;
>>>> +			pmu_count++;
>>>> +		}
>>>> +	}
>>>> +}
>>> This doesn't strike me as the right kind of structure, the presence of a
>>> compatible property really just says "hey, there's this device and it's
>>> compatible with these ways of accessing it".
>>>
>>> I'm guessing the idea behind having imc-nest-offset/size in a top level
>>> node is because it's common to everything under it and the aim is to not
>>> blow up the device tree to be enormous.
>>>
>>> So why not go after each ibm,imc-counters-nest compatible node under the
>>> top level ibm,opal-in-memory-counters node? (i'm not convinced that
>>> having ibm,ibmc-counters-nest versus ibm,imc-counters-core and
>>> ibm,imc-counters-thread as I see in the dts is correct though, as
>>> they're all accessed exactly the same way?)
>> The idea here is, we have one directory which contains common events
>> information for nest(same incase of core and thread), and one directory
>> for each nest(/core/thread) pmu.
>> So while parsing we need to make sure that the node which we are parsing
>> is the pmu node, not the node which contains the common event
>> information. We use the "compatible" property here for that purpose.
>> Because we don't have a compatible property for the node which contains
>> events info.
> That's a really bad hack.
>
> You can use the compatible property to detect the node you're looking
> for, but you need to look at the *value* of the property and check it's
> what you expect. Just checking that it's there is fragile.
>
> cheers
>



ok. I will rework this code.



Thanks,
Anju