From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wolfgang Grandegger <wg@denx.de>
Date: Wed, 16 Sep 2009 12:22:05 +0200
Subject: [U-Boot] [PATCH 2/2] fsl_i2c: Add CONFIG_FSL_I2C_CUSTOM_DFSR
In-Reply-To: <OF70C7E4F5.E49D7F47-ONC1257632.006A95E2-C1257632.006AC679@transmode.se>
References: <1253040358-30817-1-git-send-email-Joakim.Tjernlund@transmode.se>	<1253040358-30817-2-git-send-email-Joakim.Tjernlund@transmode.se>	<4AAFE249.9080604@freescale.com>	<OF18AC6068.C0F3094C-ONC1257632.0067C8BC-C1257632.00682691@transmode.se>	<4AAFE54F.7000501@freescale.com>
	<OF2D94F1B5.B1BCD01F-ONC1257632.0069CE87-C1257632.006A5EB9@transmode.se>
	<OF70C7E4F5.E49D7F47-ONC1257632.006A95E2-C1257632.006AC679@transmode.se>
Message-ID: <4AB0BC4D.1030007@denx.de>
List-Id: <u-boot.lists.denx.de>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: u-boot@lists.denx.de

Joakim Tjernlund wrote:
>> Timur Tabi <timur@freescale.com> wrote on 15/09/2009 21:04:47:
>>> Joakim Tjernlund wrote:
>>>
>>>> No, the impact on speed from DFSR is pretty small so it will
>>>> be close enough.
>>> How small?
>> From the app note:
>>   divisor = B * (A + ((3*C)/B)*2);
>>
>> C is dfsr and 10 <= A <= 30, 16 <= B <= 2048
>> Considering the actual speed may be way lower the requested speed
>> I think this is small enough.
> 
> Once we have the new procedure in place, we can calculate the exact
> divisor so the need for extra CONFIG_ options goes away.

As Timur pointed out, a new table/algorithm would require some real
testing and also some feedback from the users. Who knows if "your"
values do not make trouble. Therefore I vote for using custom
settings for maximum flexibility:

  CONFIG_FSL_I2C_CUSTOM_FDR
  CONFIG_FSL_I2C_CUSTOM_DFSR

  or

  CONFIG_FSL_I2C_CUSTOM_DFSR_FDR

Wolfgang.