Re: [PATCH/RFC 1/2] OMAP2+: powerdomain: add API to get context loss count

Paul Walmsley
2010-12-15T03:23:40Z

Hi Kevin,

working my way through these...

On Thu, 9 Dec 2010, Kevin Hilman wrote:

> Add new powerdomain API
>
> int pwrdm_get_context_loss_count(struct powerdomain *pwrdm)
>
> for checking how many times the powerdomain has lost context. The
> loss count is the sum sum of the powerdomain off-mode counter, the
> logic off counter and the per-bank memory off counter.
>
> Cc: Paul Walmsley <paul@pwsan.com>
> Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
> ---
> arch/arm/mach-omap2/powerdomain.c | 23 +++++++++++++++++++++++
> arch/arm/mach-omap2/powerdomain.h | 1 +
> 2 files changed, 24 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/powerdomain.c b/arch/arm/mach-omap2/powerdomain.c
> index 06ef60e..78e7d22 100644
> --- a/arch/arm/mach-omap2/powerdomain.c
> +++ b/arch/arm/mach-omap2/powerdomain.c
> @@ -909,3 +909,26 @@ int pwrdm_post_transition(void)
> pwrdm_for_each(_pwrdm_post_transition_cb, NULL);
> return 0;
> }
> +
> +/**
> + * pwrdm_get_context_loss_count - get powerdomain's context loss count
> + * @pwrdm: struct powerdomain * to wait for
> + *
> + * Context loss count is a sum of powerdomain off-mode counter,
> + * the logic off counter and the per-bank memory off counter.
> + */
> +int pwrdm_get_context_loss_count(struct powerdomain *pwrdm)
> +{
> + int i, count;

There should be a test here to prevent a null pointer deref if pwrdm is
NULL.

> +
> + count = pwrdm->state_counter[PWRDM_POWER_OFF];
> + count += pwrdm->ret_logic_off_counter;
> +
> + for (i = 0; i < pwrdm->banks; i++)
> + count += pwrdm->ret_mem_off_counter[i];

Looks like these state counters are unsigned ints. So they could easily
overflow count when they are summed. This is probably not a major problem
as far as this function is concerned, but the next patch can return
-ENODEV upon error, which, if this function were really unlucky, it could
effectively return -ENODEV.

It would be good to constrain the minimum successful return value of this
function to 0. This will require some creativity since the function
shouldn't just return 0 for all sums that wrap around and wind up
negative; the return value should still continue to differ from the value
when it was called previously. Otherwise devices might not restore their
context when they should.

> +
> + pr_debug("powerdomain: %s: context loss count = %u\n",
> + pwrdm->name, count);
> +
> + return count;
> +}
> diff --git a/arch/arm/mach-omap2/powerdomain.h b/arch/arm/mach-omap2/powerdomain.h
> index 35b5b48..d269eff 100644
> --- a/arch/arm/mach-omap2/powerdomain.h
> +++ b/arch/arm/mach-omap2/powerdomain.h
> @@ -211,6 +211,7 @@ int pwrdm_clkdm_state_switch(struct clockdomain *clkdm);
> int pwrdm_pre_transition(void);
> int pwrdm_post_transition(void);
> int pwrdm_set_lowpwrstchange(struct powerdomain *pwrdm);
> +int pwrdm_get_context_loss_count(struct powerdomain *pwrdm);
>
> extern void omap2xxx_powerdomains_init(void);
> extern void omap3xxx_powerdomains_init(void);

Also, as we discussed privately, there is at least one bug in the counters
where the logic-off and membank-off counters don't increment correctly
when the entire powerdomain is off. But that problem does not have to be
dealt with as part of this series...

- Paul