From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753258AbcAEUiA (ORCPT ); Tue, 5 Jan 2016 15:38:00 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:44811 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752869AbcAETqv (ORCPT ); Tue, 5 Jan 2016 14:46:51 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Cyrille Pitchen , Ludovic Desroches , Wolfram Sang , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 054/211] i2c: at91: fix write transfers by clearing pending interrupt first Date: Tue, 5 Jan 2016 11:42:42 -0800 Message-Id: <1452023119-25647-55-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1452023119-25647-1-git-send-email-kamal@canonical.com> References: <1452023119-25647-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 4.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.2.8-ckt1 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Cyrille Pitchen commit 6f6ddbb09d2a5baded0e23add3ad2d9e9417ab30 upstream. 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. Reported-by: Peter Rosin Signed-off-by: Cyrille Pitchen Signed-off-by: Ludovic Desroches Tested-by: Peter Rosin Signed-off-by: Wolfram Sang Fixes: 93563a6a71bb ("i2c: at91: fix a race condition when using the DMA controller") Signed-off-by: Kamal Mostafa --- drivers/i2c/busses/i2c-at91.c | 58 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 50 insertions(+), 8 deletions(-) diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c index 1c758cd..94c087b 100644 --- a/drivers/i2c/busses/i2c-at91.c +++ b/drivers/i2c/busses/i2c-at91.c @@ -465,19 +465,57 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) if (!irqstatus) return IRQ_NONE; - else if (irqstatus & AT91_TWI_RXRDY) - at91_twi_read_next_byte(dev); - else if (irqstatus & AT91_TWI_TXRDY) - at91_twi_write_next_byte(dev); - - /* catch error flags */ - dev->transfer_status |= status; + /* + * When a NACK condition is detected, the I2C controller sets the NACK, + * TXCOMP and TXRDY bits all together in the Status Register (SR). + * + * 1 - Handling NACK errors with CPU write transfer. + * + * In such case, we should not write the next byte into the Transmit + * Holding Register (THR) otherwise the I2C controller would start a new + * transfer and the I2C slave is likely to reply by another NACK. + * + * 2 - Handling NACK errors with DMA write transfer. + * + * By setting the TXRDY bit in the SR, the I2C controller also triggers + * the DMA controller to write the next data into the THR. Then the + * result depends on the hardware version of the I2C controller. + * + * 2a - Without support of the Alternative Command mode. + * + * This is the worst case: the DMA controller is triggered to write the + * next data into the THR, hence starting a new transfer: the I2C slave + * is likely to reply by another NACK. + * Concurrently, this interrupt handler is likely to be called to manage + * the first NACK before the I2C controller detects the second NACK and + * sets once again the NACK bit into the SR. + * When handling the first NACK, this interrupt handler disables the I2C + * controller interruptions, especially the NACK interrupt. + * Hence, the NACK bit is pending into the SR. This is why we should + * read the SR to clear all pending interrupts at the beginning of + * at91_do_twi_transfer() before actually starting a new transfer. + * + * 2b - With support of the Alternative Command mode. + * + * When a NACK condition is detected, the I2C controller also locks the + * THR (and sets the LOCK bit in the SR): even though the DMA controller + * is triggered by the TXRDY bit to write the next data into the THR, + * this data actually won't go on the I2C bus hence a second NACK is not + * generated. + */ if (irqstatus & (AT91_TWI_TXCOMP | AT91_TWI_NACK)) { at91_disable_twi_interrupts(dev); complete(&dev->cmd_complete); + } else if (irqstatus & AT91_TWI_RXRDY) { + at91_twi_read_next_byte(dev); + } else if (irqstatus & AT91_TWI_TXRDY) { + at91_twi_write_next_byte(dev); } + /* catch error flags */ + dev->transfer_status |= status; + return IRQ_HANDLED; } @@ -487,6 +525,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) unsigned long time_left; bool has_unre_flag = dev->pdata->has_unre_flag; bool has_alt_cmd = dev->pdata->has_alt_cmd; + unsigned sr; /* * WARNING: the TXCOMP bit in the Status Register is NOT a clear on @@ -537,6 +576,9 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) reinit_completion(&dev->cmd_complete); dev->transfer_status = 0; + /* Clear pending interrupts, such as NACK. */ + sr = at91_twi_read(dev, AT91_TWI_SR); + if (dev->fifo_size) { unsigned fifo_mr = at91_twi_read(dev, AT91_TWI_FMR); @@ -558,7 +600,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) } else if (dev->msg->flags & I2C_M_RD) { unsigned start_flags = AT91_TWI_START; - if (at91_twi_read(dev, AT91_TWI_SR) & AT91_TWI_RXRDY) { + if (sr & AT91_TWI_RXRDY) { dev_err(dev->dev, "RXRDY still set!"); at91_twi_read(dev, AT91_TWI_RHR); } -- 1.9.1