linux-kernel - Re: [PATCH 2/7] soc: davinci: new genpd driver

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Message-ID: <34d3980b-2c94-1540-94f0-dc0c86743475@ti.com>
Date:   Thu, 8 Feb 2018 18:26:20 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        David Lechner <david@...hnology.com>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 2/7] soc: davinci: new genpd driver

On Thursday 08 February 2018 03:24 PM, Bartosz Golaszewski wrote:
> 2018-02-08 10:30 GMT+01:00 Sekhar Nori <nsekhar@...com>:
>> On Wednesday 07 February 2018 07:15 PM, Bartosz Golaszewski wrote:
>>> +     /*
>>> +      * DaVinci always uses a single clock for power-management. We assume
>>> +      * it's the first one in the clocks property.
>>> +      */
>>> +     clk = of_clk_get(dev->of_node, 0);
>>> +     if (IS_ERR(clk))
>>> +             return PTR_ERR(clk);
>>
>> We already get this today with drivers/base/power/clock_ops.c once
>> .con_ids list is dropped from pm_clk_notifier_block (which I think it
>> should).
>>
>> If there is no reason to introduce thus functionality at this stage,
>> perhaps we should wait till such a time when its clearly needed?
>>
>> Thanks,
>> Sekhar
> 
> If I understand correctly: once we drop the con_ids list, we end up
> calling clk_get(dev, NULL) from pm_clk_acquire(), which matches
> against the clock with NULL con_id, which may not necessarily be the
> first clock in the list.

Hmm, not sure of this. In __of_clk_get_by_name() called by clk_get():

int index = 0;

/*
 * For named clocks, first look up the name in the
 * "clock-names" property.  If it cannot be found, then
 * index will be an error code, and of_clk_get() will fail.
 */
if (name)
	index = of_property_match_string(np, "clock-names", name);

So, if no con_id is provided (name == NULL), then index is set to 0
which will always get the first clock in clocks = list.

Thanks,
Sekhar