[PATCH v16 09/12] OMAP: dmtimer: low-power mode support

[Omar Ramirez Luna]

Hi Tarun,

On Tue, Sep 20, 2011 at 6:30 AM, Tarun Kanti DebBarma
<tarun.kanti at ti.com> wrote:
> Clock is enabled only when timer is started and disabled when the the timer
> is stopped. Therefore before accessing registers in functions clock is enabled
> and then disabled back at the end of access. Context save is done dynamically
> whenever the registers are modified. Context restore is called when context is
> lost.

Now that handling of the clock has been decoupled from
omap_dm_timer_request_specific/free and placed in start/stop
functions, there is a "possible irq lock inversion dependency
detected" for any attempt to enable the clock from soft|hard irq.

My use case is as follows:

DSP sends a mailbox message to ARM, this triggers a tasklet in mailbox
for processing the message, when it reaches tidspbridge it turns out
that the DSP wants to enable a gpt timer; however, locks involved
"clocks_mutex" and "dm_timer_lock" now could cause a deadlock as they
have been called from unsafe contexts in the past
(http://pastebin.com/7Dtz8t0f).

Is the intention to restrict enabling the dmtimer clocks from hard|soft irqs?

...
> @@ -303,6 +342,22 @@ void omap_dm_timer_stop(struct omap_dm_timer *timer)
>                rate = clk_get_rate(timer->fclk);
>
>        __omap_dm_timer_stop(timer, timer->posted, rate, is_omap2);
> +
> +       if (timer->loses_context) {
> +               if (timer->get_context_loss_count)
> +                       timer->ctx_loss_count =
> +                       timer->get_context_loss_count(&timer->pdev->dev);
> +       }
> +
> +       /*
> +        * Since the register values are computed and written within
> +        * __omap_dm_timer_stop, we need to use read to retrieve the
> +        * context.
> +        */
> +       timer->context.tclr =
> +                       omap_dm_timer_read_reg(timer, OMAP_TIMER_CTRL_REG);
> +       timer->context.tisr = __raw_readl(timer->irq_stat);
> +       omap_dm_timer_disable(timer);
>  }
>  EXPORT_SYMBOL_GPL(omap_dm_timer_stop);
>

I didn't review the whole patch, but at least this part is not in
mainline, it seems like the patch modified by Tony and the v16 were
not the same.

I could diff and include the missing parts, if someone can confirm
that we need v16, which I believe so, since current stop function
doesn't call omap_dm_timer_disable.

Regards,

Omar