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

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]

Message-ID: <CAMAWPa94ZesenozT4zLQ7ihCUVE6BwKpPQxz-6ao9iSM2t9BDA@mail.gmail.com>
Date:	Wed, 27 Aug 2014 11:39:15 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Nishanth Menon <nm@...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 11:35 AM, Nishanth Menon <nm@...com> wrote:
> 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..

WARN, pr_warn() as you like.

The point is that BUG* calls panic() and locks up the system tight.
As what your'e adding is not fatal to the entire system, you should
not be using bug.  From asm-generic/bug.h:

*
 * Don't use BUG() or BUG_ON() unless there's really no way out; one
 * example might be detecting data structure corruption in the middle
 * of an operation that can't be backed out of.  If the (sub)system
 * can somehow continue operating, perhaps with reduced functionality,
 * it's probably not BUG-worthy.
 *
 * If you're tempted to BUG(), think again:  is completely giving up
 * really the *only* solution?  There are usually better options, where
 * users don't need to reboot ASAP and can mostly shut down cleanly.
 */
--
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/