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

From: Kevin Hilman
Date: Wed Aug 27 2014 - 14:39:23 EST

On Wed, Aug 27, 2014 at 11:35 AM, Nishanth Menon <nm@xxxxxx> wrote:
> On Wed, Aug 27, 2014 at 1:27 PM, Kevin Hilman
> <khilman@xxxxxxxxxxxxxxxxxxx> wrote:
>> Nishanth Menon <nm@xxxxxx> 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@xxxxxx>
>>> . 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:
>>> Signed-off-by: Nishanth Menon <nm@xxxxxx>
>>> ---
>> 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@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at