From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wolfgang Grandegger <wg@denx.de>
Date: Thu, 17 Sep 2009 08:36:32 +0200
Subject: [U-Boot] [PATCH 2/2] fsl_i2c: Add CONFIG_FSL_I2C_CUSTOM_DFSR
In-Reply-To: <OF37706726.BC369064-ONC1257633.00434B57-C1257633.00437D52@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>	<4AB0BC4D.1030007@denx.de>
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	<4AB0CFBF.2050009@grandegger.com>
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Joakim Tjernlund wrote:
> Wolfgang Grandegger <wg@grandegger.com> wrote on 16/09/2009 13:45:03:
>> Joakim Tjernlund wrote:
>>> Wolfgang Grandegger <wg@denx.de> wrote on 16/09/2009 12:22:05:
>>>> 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
>>> Oh well, since you both wanted it I added it.
>>> Sent 3 patches, the last patch impl. the latest AN2819 spec.
>>>
>>> Would you mind test it a little?
>> OK, I will do some tests later this week. What CPU do you use and at
>> what I2C bus frequency do you test?
> 
> mpc8321, I2C bus is between 34KHz and 100KHz, CSB is 133.332 MHz

OK, where can I find the new AN2819? I found Document Number: AN2919,
Rev. 5, 12/2008.

Wolfgang.