linux-kernel - Re: [PATCH] bus: arm-cci: constify attribute

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Date:   Thu, 6 Jul 2017 09:41:58 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Arvind Yadav <arvind.yadav.cs@...il.com>, nico@...aro.org,
        mark.rutland@....com, mingo@...nel.org, lorenzo.pieralisi@....com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bus: arm-cci: constify attribute_group structures.

On 06/07/17 05:53, Arvind Yadav wrote:
> Hi,
>
>
> On Wednesday 05 July 2017 09:33 PM, Suzuki K Poulose wrote:
>> On 03/07/17 08:46, Arvind Yadav wrote:
>>> attribute_groups are not supposed to change at runtime. All functions
>>> working with attribute_groups provided by <linux/sysfs.h> work with const
>>> attribute_group. So mark the non-const structs as const.
>>>
>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>>> ---
>>>  drivers/bus/arm-cci.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
>>> index c49da15..64c75d2 100644
>>> --- a/drivers/bus/arm-cci.c
>>> +++ b/drivers/bus/arm-cci.c
>>> @@ -1445,16 +1445,16 @@ static ssize_t pmu_cpumask_attr_show(struct device *dev,
>>>      NULL,
>>>  };
>>>
>>> -static struct attribute_group pmu_attr_group = {
>>> +static const struct attribute_group pmu_attr_group = {
>>>      .attrs = pmu_attrs, /*This can be const*/
>>>  };
>>>
>>> -static struct attribute_group pmu_format_attr_group = {
>>> +static const struct attribute_group pmu_format_attr_group = {
>>>      .name = "format",
>>>      .attrs = NULL,        /* Filled in cci_pmu_init_attrs */
>>>  };
>>
>>
>>
>>>
>>> -static struct attribute_group pmu_event_attr_group = {
>>> +static const struct attribute_group pmu_event_attr_group = {
>>>      .name = "events",
>>>      .attrs = NULL,        /* Filled in cci_pmu_init_attrs */
>>>  };
>>>
>>
>> I think we cannot make these const, as the attrs field gets filled in at runtime, indicated
>> by the comments next to them.
>>
>     Yes, Your are right. It's filled at run time.
>         pmu_event_attr_group.attrs = model->event_attrs;
>         pmu_format_attr_group.attrs = model->format_attrs;
>     can we make pmu_attr_group as const.? It's already initialized.
>     If you are ok with this please let me know. I can push updated patch.
>

Yes, you can do that.

Or you could go a step ahead and create per-model pmu_attr_groups[], with shared
pmu_attr_group and per-model event/format groups and tie it to the model description
and make everything const.

i.e,

static const struct attribute_group cci5xx_pmu_attr_groups[] = {
	&pmu_attr_group,
	&cci5xx_format_attr_group,
	&cci5xx_event_attr_group,
	NULL,
};

static const struct attribute_group cci400r0_pmu_attr_groups = {
	&pmu_attr_group,
	&cci400_pmu_format_attr_group,
	&cci400_pmu_event_attr_group,
	NULL,
};

static const struct attribute_group cci400r1_pmu_attr_groups = {
	&pmu_attr_group,
	&cci400_pmu_format_attr_group,
	&cci400r1_pmu_event_attr_group,
	NULL,
};

and then do :

cci_pmu->pmu = (struct pmu) {
	....
	.attr_groups = model->attr_groups,
};

Suzuki