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. > > 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 U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot