On Wed, 2017-05-10 at 20:42 -0500, Scott Wood wrote: > On Wed, 2017-05-10 at 07:02 +0000, Joakim Tjernlund wrote: > > On Tue, 2017-05-09 at 15:54 -0500, Scott Wood wrote: > > > On Tue, May 09, 2017 at 02:03:51PM +0200, Joakim Tjernlund wrote: > > > > Current I2C reset procedure is broken in two ways: > > > > 1) It only generate 1 START instead of 9 STARTs and STOP. > > > > 2) It leaves the bus Busy so every I2C xfer after the first > > > > fixup calls the reset routine again, for every xfer there after. > > > > > > > > This fixes both errors. Add an iobarrier_rw() when writing the > > > > I2C control register as well to make sure the register reaches the > > > > controller in time. > > > > > > > > Signed-off-by: Joakim Tjernlund <joakim.tjernlund@xxxxxxxxxxxx> > > > > --- > > > > > > > > Not sure where to sent this as there is no maintainer so adding > > > > Scott Wood as well. > > > > > > > > drivers/i2c/busses/i2c-mpc.c | 24 ++++++++++++++++-------- > > > > 1 file changed, 16 insertions(+), 8 deletions(-) > > > > > > > > diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c > > > > index 8393140..09b826d 100644 > > > > --- a/drivers/i2c/busses/i2c-mpc.c > > > > +++ b/drivers/i2c/busses/i2c-mpc.c > > > > @@ -86,6 +86,7 @@ struct mpc_i2c_data { > > > > static inline void writeccr(struct mpc_i2c *i2c, u32 x) > > > > { > > > > writeb(x, i2c->base + MPC_I2C_CR); > > > > + iobarrier_rw(); > > > > } > > > > > > Why are the barriers in the I/O accessors insufficient? > > > > You mean writeb()? As far as I can see the writeb/readb only uses volatile > > and that > > can be a bit weak for ppc, even on guarded, uncached memory mappings. > > I wanted to make sure multiple writeb did hit the controller correctly. > > It's not just a volatile. There's a sync before each access, and a twi/isync > after loads. writeb() maps to __do_writeb() which maps to out_8() which is > implemented with DEF_MMIO_OUT_D. ehh, right you are. That was some very complicated include/#ifdef trickery to go through. I will send an update patch with the iobarrier_rw() removed. Jocke-- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html