linux-kernel - Re: [RFC PATCH 1/2] regulator: core: Add regulator_set_voltage

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 23 Apr 2013 21:45:09 +0300
From:	Taras Kondratiuk <taras@...com>
To:	Mark Brown <broonie@...nel.org>
CC:	<lgirdwood@...il.com>, <rjw@...k.pl>, <viresh.kumar@...aro.org>,
	<shawn.guo@...aro.org>, <cpufreq@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Philip Rakity <prakity@...dia.com>,
	Eric Miao <eric.y.miao@...il.com>,
	"grygorii.strashko" <grygorii.strashko@...com>,
	Andrii Tseglytskyi <andrii.tseglytskyi@...com>
Subject: Re: [RFC PATCH 1/2] regulator: core: Add regulator_set_voltage_min()

On 04/23/2013 04:45 PM, Mark Brown wrote:
> On Tue, Apr 23, 2013 at 02:44:58PM +0300, Taras Kondratiuk wrote:
>
>> GPU voltage is regulated by some devfreq driver.
>> CPU voltage is regulated by generic cpufreq-cpu0 driver.
>> Both drivers know only about their operational points.
>> They don't know anything about chip limits.
> Clearly at least the lower bound is known to the drivers...
Do you mean a voltage of the lowest operation point?

>
>> I see two options here:
>> 1. Pass somehow chip limits to drivers so they can limit their request.
>>     Pros: No need for regulator_set_voltage_min()
>>     Cons: a) Need to pass info about chip limits to driver. New API?
> Why on earth would this need a new API?
I think I'm missing something.
How can I pass chip limits to a driver in some generic way?
>
>>           b) CPU and GPU may have different limits,
>>              so after very first request voltage may violate
>>              CPU or GPU range.
> If the CPU and GPU drivers are trying to select incompatible
> configurations then we really ought to be detecting that, ignoring it
> seems like an obvious failure.  There's a bootstrapping problem but
> that's also an issue with specifying only the minimum voltage...
>
>> 2. Define chip limits in Reg X constraints.
>>     Pros: Limits will be applied to driver's request transparently.
>>           No need to pass info about limits to driver.
>>           Limits are set before the first request, so no violation.
>>     Cons: regulator_set_voltage_min() is needed.
>> IMHO option #2 is better.
>> Do you see other ways?
> Above you clearly say that this is all modelling operating points.  If
> you're doing that then I would expect the drivers to be talking
> operating points to an operating point abstraction.
I went through several SoC datasheets and found that min approach
won't work for some of them (like AM335x).
The only safe way is to send max OPP voltage as a max_uV.
So please skip this series.

-- 
BR
Taras Kondratiuk | GlobalLogic

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/