Subject: Re: [PATCH v3 5/5] powerpc/85xx: i2c-mpc: use new I2C bindings for the Socates board

From: Wolfgang Grandegger <[email-masked]>
Date: Wed, 08 Apr 2009 20:27:12 +0200

Grant Likely wrote:
> On Wed, Apr 8, 2009 at 12:16 AM, Wolfgang Grandegger <[email-masked]> wrote:
>> Grant Likely wrote:
>>> On Tue, Apr 7, 2009 at 1:20 AM, Wolfgang Grandegger <[email-masked]> wrote:
>>>> Preserve I2C clock settings for the Socrates MPC8544 board.
>>> I had thought that the preserve-clocking property was intended for
>>> older boards that don't currently have any method of getting the clock
>>> setting out of u-boot.  Since Socrates is a new board, U-Boot should
>>> probably be made to fill in the real clock rate setting.
>> I'm not sure if I understand what you mean. If an old version of U-Boot
>> on an old board sets the I2C clock, it can be used (inherited) by Linux
>> using the property "preserve-clocking".
>>
>> It is actually the customers choice to set the I2C clock in U-Boot and
>> re-use it by Linux.
> 
> Setting it in the register != recording the value in the device tree.
> I'm saying that since Socrates is a new board it should not use the
> preserve-clocking dirty trick (and it is a dirty trick) because the
> correct clocking data can be passed via the device tree.

Why should an old board then use it. "fsl, preserve-clocking" is a new
feature, like using "clock-frequency" and you have the choice to
explicitly set the clocking via device tree or inherit it from the boot
loader. So far, a fixed FDR/DFRSS value (0x1031) was written to the
registers by Linux.

Wolfgang.