Re: [RFC v2]: Issues implementing clock handling mechanism within UART driver

Felipe Balbi
2011-07-29T12:19:13Z

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Hi,

On Fri, Jul 29, 2011 at 05:29:12PM +0530, Govindraj wrote:
> Yes fine, But there are scenarios even before first runtime_suspend happens,
>
> ex: uart_port_configure -> get_sync -> pm_generic_runtime_resume
> (omap_device_enable in this case) debug printk -> console_write -> get_sync.
>
> there are numerous such scenarios where we end from runtime context
> to runtime api context again, or jumping from one uart port operation
> to uart print operation.

calling pm_runtime_get_sync() should not be a problem. It should only
increase the usage counters... This sounds like a race condition on the
driver, no ?

What you're experiencing, if I understood correctly, is a deadlock ? In
that case, can you try to track the locking mechanism on the omap-serial
driver to try to find if there isn't anything obviously wrong ?

> So either we should not have those prints from pm_generic layers or suppress
> them(seems pretty much a problem for a clean design within the driver
> using console_lock/unlock for every get_sync, and for
> runtime_put we cannot suppress the prints as it gets scheduled later)
>
> or if other folks who really need those prints form pm_generic* layers
> to debug and analysis then we have no other choice rather control
> the clk_enable/disable from outside driver code in idle path.

yeah, none of these would be nice :-(

I think this needs more debugging to be sure what's exactly going on.
What's exactly causing the deadlock ? Which lock is held and never
released ?

--
balbi

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