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

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Date:   Thu, 8 Feb 2018 20:13:06 +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 06:57 PM, Bartosz Golaszewski wrote:
> 2018-02-08 13:56 GMT+01:00 Sekhar Nori <nsekhar@...com>:
>> 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.
>>
> 
> But we're talking here about device tree mode. In legacy mode the
> device_node pointer will be NULL, __of_clk_get_by_name() will return
> -ENOENT and we'll end up calling clk_get_sys() -> clk_find(). We'll
> then iterate over the clock entries and check the following:
> 
> (...)
> 152                 if (p->con_id) {
> 153                         if (!con_id || strcmp(p->con_id, con_id))
> 154                                 continue;
> 155                         match += 1;
> 156                 }
> (...)
> 
> So we'll skip the first clock if it has a con_id and we passed an
> empty con_id to clk_get().

You are right. I missed taking the effect on legacy boot into
consideration. Please send v2 then, and consider this objection withdrawn.

Thanks,
Sekhar