On 06/26/2014 01:18 PM, Stephen Warren wrote: > On 06/26/2014 01:11 PM, Joakim Tjernlund wrote: >> Stephen Warren <swar...@wwwdotorg.org> wrote on 2014/06/26 18:47:55: >>> >>> On 06/26/2014 02:11 AM, Joakim Tjernlund wrote: >>>>> From: Stephen Warren <swar...@wwwdotorg.org> >>>>> To: u-boot@lists.denx.de, Heiko Schocher <h...@denx.de>, >>>>> Cc: Stephen Warren <swar...@nvidia.com>, Tom Warren >> <twar...@nvidia.com> >>>>> Date: 2014/06/25 19:05 >>>>> Subject: [U-Boot] [PATCH 1/3] i2c: tegra: use repeated start for >> reads >>>>> Sent by: u-boot-boun...@lists.denx.de >>>>> >>>>> From: Stephen Warren <swar...@nvidia.com> >>>>> >>>>> I2C read transactions are typically implemented as follows: >>>>> >>>>> START(write) address REPEATED_START(read) data... STOP >>>>> >>>>> However, Tegra's I2C driver currently implements reads as follows: >>>>> >>>>> START(write) address STOP START(read) data... STOP >>>>> >>>>> This sequence confuses at least the AS3722 PMIC on the Jetson TK1 >> board, >>>>> leading to corrupted read data in some cases. Fix the driver to chain >>>>> the transactions together using repeated starts to solve this. >>>> >>>> While I agree to use Repeated START I just wanted to share this: >>>> A common reason for STOP START(read) sequence not working sometimes is >> >>>> that >>>> the driver initializes STOP but does not wait for the STOP to complete >>>> before issuing a START. >>> >>> I don't believe that's the case here, since all this patch does is set a >>> flag to indicate whether the write transaction (to set the intra-chip >>> register address) generates STOP or REPEATED_START at the end. If the >>> code or HW wasn't waiting for the STOP to complete, I see no reason it >>> would wait for the REPEATED_START to complete either, so I think the >>> subsequent register read transaction would be corrupted in either case. >> >> But there is, you have STOP + START vs. ReSTART only and if the code only >> flips a flag to change I think there is a chance in this case. >> You could easily test by adding a udelay(5) after STOP is initiated.
The delay makes no difference. (I delayed 1ms). _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
