Hi Wolfram, On Thursday 03 September 2015 22:20:04 Wolfram Sang wrote: > Hello RCar Fans! > > Two issues people have seen with the i2c-rcar driver was: > > a) immediately restarted messages after NACK from client > b) duplicated data bytes in messages > > Some people already worked on those and had a tough time because it was hard > to reproduce these issues on non-customer setup. Luckily, I somewhen had a > state where the first transfer after boot would always show the above > issues on a plain Renesas Lager board. When measuring, I found a third > issue thanks to my new tool 'i2ctransfer' (and thanks to projects like > sigrok and OpenLogicSniffer, of course. Thank you very much!): > > c) after read message, no repeated start was sent, but stop + start. > > Due to some unlucky design choices in the IP core, it has some race windows > which can cause problems if interrupts get delayed. Also, for every new > message in one transfer, context switches between interrupt and process > were needed. > > So I refactored the driver to setup new messages in interrupt context, too. > This avoids the race for b) because we are now setting up the new message > before we release the i2c bus clock (before we released the clock and set up > the message in process context). Could this fix the HDMI EDID read issue on Koelsch ? > c) is also fixed, this was not a race but a bug in the state handling. a) > however is not fixed 100% :( We have the race window as small as possible > now when utilizing interrupts, so it is an improvement and worked for my > test cases well. There were experiments by me and Renesas engineers to use > polling to prevent the issue but this caused other side effects, sadly. So, > let's improve the situation now and let's see where we get. Does that mean that, due to hardware design, it's impossible to use I2C interrupts in a race-free way ? It would be interesting to document why in a commit log message, or possibly in the code itself. > I did quite some lab testing here and also verified that slave support does > not suffer from these changes. However, I'd really appreciate if people > could give this real-world-testing which is always different. > > Please have a look, a test, etc... > > Thanks, > > Wolfram > > > Wolfram Sang (9): > i2c: rcar: rework hw init > i2c: rcar: remove unused IOERROR state > i2c: rcar: remove spinlock > i2c: rcar: refactor setup of a msg > i2c: rcar: init new messages in irq > i2c: rcar: don't issue stop when HW does it automatically > i2c: rcar: check master irqs before slave irqs > i2c: rcar: revoke START request early > i2c: rcar: clean up after refactoring > > drivers/i2c/busses/i2c-rcar.c | 193 +++++++++++++++------------------------ > 1 file changed, 71 insertions(+), 122 deletions(-) -- Regards, Laurent Pinchart -- 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
