From mboxrd@z Thu Jan 1 00:00:00 1970 From: wsa@the-dreams.de (Wolfram Sang) Date: Thu, 22 Oct 2015 15:07:35 +0200 Subject: [PATCH v2 1/2] i2c: at91: fix write transfers by clearing pending interrupt first In-Reply-To: <1445435048-25889-1-git-send-email-ludovic.desroches@atmel.com> References: <1445435048-25889-1-git-send-email-ludovic.desroches@atmel.com> Message-ID: <20151022130735.GD1517@katana> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Oct 21, 2015 at 03:44:03PM +0200, Ludovic Desroches wrote: > From: Cyrille Pitchen > > In some cases a NACK interrupt may be pending in the Status Register (SR) > as a result of a previous transfer. However at91_do_twi_transfer() did not > read the SR to clear pending interruptions before starting a new transfer. > Hence a NACK interrupt rose as soon as it was enabled again at the I2C > controller level, resulting in a wrong sequence of operations and strange > patterns of behaviour on the I2C bus, such as a clock stretch followed by > a restart of the transfer. > > This first issue occurred with both DMA and PIO write transfers. > > Also when a NACK error was detected during a PIO write transfer, the > interrupt handler used to wrongly start a new transfer by writing into the > Transmit Holding Register (THR). Then the I2C slave was likely to reply > with a second NACK. > > This second issue is fixed in atmel_twi_interrupt() by handling the TXRDY > status bit only if both the TXCOMP and NACK status bits are cleared. > > Tested with a at24 eeprom on sama5d36ek board running a linux-4.1-at91 > kernel image. Adapted to linux-next. > > Signed-off-by: Cyrille Pitchen > Fixes: 93563a6a71bb ("i2c: at91: fix a race condition when using the DMA controller") > Reported-by: Peter Rosin > Signed-off-by: Ludovic Desroches > Tested-by: Peter Rosin > Cc: stable at vger.kernel.org #4.1 Applied to for-next, thanks! I considered for-current, but really want this to sit a little in for-next to make sure there are no regressions. It will go back via stable. -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: