linux-kernel - Re: [PATCH 4/7] ARM: OMAP2+: powerdomain: introduce logic for finding valid power domain

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Date:	Wed, 27 Aug 2014 13:35:46 -0500
From:	Nishanth Menon <nm@...com>
To:	Kevin Hilman <khilman@...prootsystems.com>
Cc:	Paul Walmsley <paul@...an.com>, Tony Lindgren <tony@...mide.com>,
	Keerthy <j-keerthy@...com>, lkml <linux-kernel@...r.kernel.org>,
	Tero Kristo <t-kristo@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Benoît Cousson <bcousson@...libre.com>,
	linux-omap <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/7] ARM: OMAP2+: powerdomain: introduce logic for finding
 valid power domain

On Wed, Aug 27, 2014 at 1:27 PM, Kevin Hilman
<khilman@...prootsystems.com> wrote:
> Nishanth Menon <nm@...com> writes:
>
>> powerdomain configuration in OMAP is done using PWRSTCTRL register for
>> each power domain. However, PRCM lets us write any value we'd like to
>> the logic and power domain target states, however the SoC integration
>> tends to actually function only at a few discrete states. These valid
>> states are already in our powerdomains_xxx_data.c file.
>>
>> So, provide a function to easily query valid low power state that the
>> power domain is allowed to go to.
>>
>> Based on work originally done by Jean Pihet <j-pihet@...com>
>> https://patchwork.kernel.org/patch/1325091/ . There is no attempt to
>> create a new powerdomain solution here, except fixing issues seen
>> attempting invalid programming attempts. Future consolidation to the
>> generic powerdomain framework should consider this requirement as
>> well.
>>
>> Similar solutions have been done in product kernels in the past such
>> as:
>> https://android.googlesource.com/kernel/omap.git/+blame/android-omap-panda-3.0/arch/arm/mach-omap2/pm44xx.c
>>
>> Signed-off-by: Nishanth Menon <nm@...com>
>> ---
>
> nit: this is part of a fixes series, but it's more of a new feature.
>
> That being said, the feature is needed and looks OK, except for...
>
>> +up_search:
>> +     /* OK, no deeper ones, can we get a higher match? */
>> +     new_pwrst = req_state + 1;
>> +     while (!(pwrdm_states & BIT(new_pwrst))) {
>> +             /* BUG if we have messed up database */
>> +             BUG_ON(new_pwrst > PWRDM_POWER_ON);
>
> I don't think this is BUG() worthy, and should have a saner way to recover.

it is not even a legal value to have a power state higher than ON. I
mean, yeah, we can do
if (new_pwrst > PWRDM_POWER_ON) {
         pr_debug("powerdomain: %s: fix my powerdomain max to ON\n",
pwrdm->name);
         return PWRDM_POWER_ON;
}

if that is your suggestion here, personally, I would use a WARN at least here..

-- 
---
Regards,
Nishanth Menon
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