netdev - Re: [PATCH] use cond_resched() to replace udelay() when dump eeprom

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Date:	Tue, 13 May 2014 22:41:29 -0700
From:	Michael Chan <mchan@...adcom.com>
To:	David Miller <davem@...emloft.net>
CC:	<acho@...e.com>, <netdev@...r.kernel.org>, <bpoirier@...e.de>
Subject: Re: [PATCH] use cond_resched() to replace udelay() when dump eeprom

On Wed, 2014-05-14 at 00:53 -0400, David Miller wrote: 
> From: Michael Chan <mchan@...adcom.com>
> Date: Mon, 12 May 2014 10:48:30 -0700
> 
> > We still need to time these commands.  Using cond_resched(), the timing
> > becomes unpredictable.  Perhaps we can reduce the NVRAM_CMD_TIMEOUT
> > counter by a factor of 100 and use msleep(1) instead of udelay(10).
> 
> That should work.

It actually won't work very well.  It typically takes 10 to 20 us to
read one 32-bit value.  Using msleep(1), it will take 100 times longer
than it should.  When dumping the entire NVRAM, it will visibly take a
very long time.

We are working on a patch to make sure that the clock is not running
slow when reading the NVRAM.  I think we can also reduce
NVRAM_CMD_TIMEOUT to something more reasonable.

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