From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfgang Grandegger Date: Mon, 21 Sep 2009 13:59:04 +0200 Subject: [U-Boot] [PATCH 3/3] fsl_i2c: Impl. AN2919, rev 5 to calculate FDR/DFSR In-Reply-To: References: <1253178437-32398-1-git-send-email-Joakim.Tjernlund@transmode.se> <1253178437-32398-2-git-send-email-Joakim.Tjernlund@transmode.se> <1253178437-32398-3-git-send-email-Joakim.Tjernlund@transmode.se> <4AB75B30.4030004@denx.de> Message-ID: <4AB76A88.4060700@denx.de> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Joakim Tjernlund wrote: > Wolfgang Grandegger wrote on 21/09/2009 12:53:36: >> Hi Joakim, >> >> Joakim Tjernlund wrote: >>> The latest AN2919 has changed the way FDR/DFSR should be calculated. >>> Update the driver according to spec. However, Condition 2 >>> is not accounted for as it is not clear how to do so. >> I compared rev. 5 of AN2919 with rev. 3 and, as you pointed out, it puts >> additional constraints on how to select dfsr and fdr. Especially dfsr >> should not exceed a certain, frequency dependent value: dfsr <= 50 / >> period-in-ns. Therefore, I expected problems with divider values from >> the table which high dfsr values. I did your "=> date;date;date;date" >> test on a MPC8548 board using dfsr=43 and fdr=7 but it did not fail. >> According to the rev. 5, dfsr is not allowed to be greater than 8. >> Your patch works fine on this board as well. I have no time for a more >> thorough testing with different CPUs and frequencies. Anyhow... > > Yes, I too notice that higher dfsr values than the spec says works, in > fact my board needs at least dfsr 8 to be 100% stable but the spec says > no more that 6 for my board. I suspect that we should enforce a minimum > value of 8 to be on the safe side, especially as the HW default is 0x10. You say that the new constraints introduced by rev. 5 are not even correct!? Well, these modifications are obscure anyhow. > Anyhow it is better now than before. At least for your board. Let's keep an eye on people reporting I2C problems for these processors on the U-Boot and linuxppc-dev ML. Wolfgang.