linux-kernel - Re: [PATCH v2 1/3] net: irda: pxaficp_ir: use sched

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Date:	Wed, 16 Sep 2015 11:34:01 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	David Miller <davem@...emloft.net>
Cc:	samuel@...tiz.org, petr.cvek@....cz, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, arnd@...db.de
Subject: Re: [PATCH v2 1/3] net: irda: pxaficp_ir: use sched_clock() for time management

David Miller <davem@...emloft.net> writes:

> From: Robert Jarzmik <robert.jarzmik@...e.fr>
> Date: Sat, 12 Sep 2015 13:45:22 +0200
>
>> Instead of using directly the OS timer through direct register access,
>> use the standard sched_clock(), which will end up in OSCR reading
>> anyway.
>> 
>> This is a first step for direct access register removal and machine
>> specific code removal from this driver.
>> 
>> Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
>
> What is the granularity of the OSCR register?
It's 307ns (ie. 3.25MHz clock).

> If it is not nanoseconds, then you need to adjust calculations
> such as this one:
Tell me if the 307ns requires something I should adjust.

My understanding is that the flow will be :
 sched_clock()
   rd->read_sched_clock() (cyc_to_ns() transformed for return)
     pxa_read_sched_clock()
       readl_relaxed(OSCR)

I didn't see any timings issue, as the flow looks equivalent to the readl(OSCR),
but I might have overlooked something.

Cheers.

-- 
Robert
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