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From: Scott Wood <scottwood@freescale.com>
To: Trent Piepho <tpiepho@freescale.com>
Cc: "André Schwarz" <Andre.Schwarz@matrix-vision.de>,
	"Timur Tabi" <timur@freescale.com>,
	linuxppc-dev@ozlabs.org
Subject: Re: i2c-mpc clocking scheme
Date: Mon, 01 Dec 2008 17:07:16 -0600	[thread overview]
Message-ID: <49346E24.7090002@freescale.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0812011438550.10176@t2.domain.actdsltmp>

Trent Piepho wrote:
> The Linux code could use current-speed to know if it should program the
> registers.  I.e., if current-speed is present and non-zero, then leave the
> frequency registers alone.  Otherwise u-boot or whatever might not have
> programmed the I2C controller and the driver can do what it's doing now.

I suppose.  I was thinking that Linux could just check to see whether 
the current divider value appears to be valid, but it seems that all 
values including zero can be valid. :-(

>> When does the guest really care what the specific i2c bus frequency is, if 
>> it's not going to change it?
> 
> I don't know of a real reason.  Maybe an I2C device where the clock speed
> makes a difference?  Maximum polling rate or something?  Is there reason
> the CPU clock and the CCB frequency need to be in the device tree?

I'm fine with including it for informational purposes, it just doesn't 
seem quite as necessary.

-Scott

  parent reply	other threads:[~2008-12-01 23:09 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-27 15:00 i2c-mpc clocking scheme Andre Schwarz
2008-11-27 15:24 ` Timur Tabi
2008-11-27 15:43   ` Andre Schwarz
2008-11-28 20:59     ` Trent Piepho
2008-12-01 14:59       ` Timur Tabi
2008-12-01 19:40         ` André Schwarz
2008-12-01 19:48           ` Timur Tabi
2008-12-01 22:07           ` Trent Piepho
2008-12-01 22:26             ` Scott Wood
2008-12-01 22:57               ` Trent Piepho
2008-12-01 23:00                 ` Timur Tabi
2008-12-01 23:07                 ` Scott Wood [this message]
2008-11-27 15:49   ` Luotao Fu

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