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

Kevin Hilman khilman at deeprootsystems.com
Wed Aug 27 11:39:15 PDT 2014

On Wed, Aug 27, 2014 at 11:35 AM, Nishanth Menon <nm at ti.com> wrote:
> On Wed, Aug 27, 2014 at 1:27 PM, Kevin Hilman
> <khilman at deeprootsystems.com> wrote:
>> Nishanth Menon <nm at ti.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 at ti.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 at ti.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.

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