linux-kernel - Re: [PATCH v4 3/8] clk: add support for clocks provided by SCP(System Control Processor)

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Message-ID: <55A8E434.2010709@arm.com>
Date:	Fri, 17 Jul 2015 12:17:08 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
CC:	Sudeep Holla <sudeep.holla@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Kevin Hilman <khilman@...nel.org>,
	Olof Johansson <olof@...om.net>,
	Mike Turquette <mturquette@...libre.com>
Subject: Re: [PATCH v4 3/8] clk: add support for clocks provided by SCP(System
 Control Processor)



On 16/07/15 20:31, Stephen Boyd wrote:
> On 07/16, Sudeep Holla wrote:
>> On 08/07/15 02:46, Stephen Boyd wrote:
>>>
>>> Yes struct clk would have min/max, and struct clk_core would have
>>> min/max. Then some sort of provider API (or possibly even
>>> clk_init_data) would take the min/max fields and copy them over
>>> to struct clk_core. Then during set_rate operations we would
>>> aggregate the constraints from struct clk like we already do and
>>> add in the constrains in struct clk_core.
>>>
>>> One downside to adding new fields to clk_init_data is that there
>>> are drivers out there that aren't initializing that structure to
>>> 0, and they're putting it on the stack, so stack junk can come
>>> through. Furthermore, min/max would mean that every driver needs
>>> to specify some large number for max or we have to special case
>>> min == max == 0 and ignore it. Somehow it needs to be opt-in. If
>>> we want to go down the clk_init_data route then perhaps we need
>>> some sort of rate_constraint struct pointer in there that drivers
>>> can optionally setup.
>>>
>>> 	struct clk_rate_constraint {
>>> 		unsigned long min;
>>> 		unsigned long max;
>>> 	};
>>>
>>> 	struct clk_init_data {
>>> 		...
>>> 		struct clk_rate_constraint *rate_constraint;
>>> 	};
>>>
>>> I haven't thought it through completely, but I can probably write
>>> up some patch tomorrow after I sleep on it.
>>>
>>
>> I am hoping to get this series for v4.3. In order to avoid using
>> consumer API, I can revert back to the min,max check I had in the
>> round_rate earlier if that's fine with you ? Let me know so that I can
>> post the next version based on that. All the other comments are already
>> addressed.
>
> Ok. I'm fine with the consumer API being used, but it would be
> nice if we didn't have to do so. Try out the patch below,
> hopefully it's good enough for your purposes. It may need to be
> more robust, and we may still want to use the init_data structure
> to avoid races with providers and consumers, but we can leave
> that for later after sweeping all the structure users.
>

Agreed, I would avoid using clk consumer API or use it with TODO so that
I remember to remove it soon. Anyways, thanks for the patch, I tested it
and works fine to me. You can add Tested-by if you decide to push it.

>>
>> Also since this series depends on SCPI, I was thinking to get it merged
>> via ARM-SoC, but that might conflict with the round_rate prototype
>> change. Do do plan to share a stable base with arm-soc guys or you
>> expect all the changes to be contained in clk tree ?
>>
>
> We can share a stable branch for the determine_rate change with
> arm-soc. We already have it on a separate branch but haven't
> published it so far because nobody has asked.
>

determine_rate change shouldn't affect SCPI clock driver but I remember
seeing round_rate change too on the list which returns value using the
argument from Boris. Is that planned for v4.3 ? I would need the stable
branch from this clk_hw_set_rate_range if you decide to push. Let me
know your preferences. I will post the updated version of the patch
accordingly.

Regards,
Sudeep
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