On 06/26/2014 02:11 AM, Joakim Tjernlund wrote: >> From: Stephen Warren <[email protected]> >> To: [email protected], Heiko Schocher <[email protected]>, >> Cc: Stephen Warren <[email protected]>, Tom Warren <[email protected]> >> Date: 2014/06/25 19:05 >> Subject: [U-Boot] [PATCH 1/3] i2c: tegra: use repeated start for reads >> Sent by: [email protected] >> >> From: Stephen Warren <[email protected]> >> >> 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. There's certainly code in tegra_i2c.c:wait_for_transfer_complete() to poll until each transaction completes before starting the next, and there's even error handling to detect any problems there:-) _______________________________________________ U-Boot mailing list [email protected] http://lists.denx.de/mailman/listinfo/u-boot
