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Commit a9bed6b1 authored by Ludovic Desroches's avatar Ludovic Desroches Committed by Wolfram Sang
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i2c: at91: manage unexpected RXRDY flag when starting a transfer 



In some cases, we could start a new i2c transfer with the RXRDY flag
set. It is not a clean state and it leads to print annoying error
messages even if there no real issue. The cause is only having garbage
data in the Receive Holding Register because of a weird behavior of the
RXRDY flag.

Reported-by: default avatarPeter Rosin <peda@lysator.liu.se>
Signed-off-by: default avatarLudovic Desroches <ludovic.desroches@atmel.com>
Tested-by: default avatarPeter Rosin <peda@lysator.liu.se>
Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>
Fixes: 93563a6a ("i2c: at91: fix a race condition when using the DMA controller")
Cc: stable@vger.kernel.org #4.1
parent 43e9f2aa

drivers/i2c/busses/i2c-at91.c

+26 −10
Original line number Diff line number Diff line
@@ -347,8 +347,14 @@ static void at91_twi_write_data_dma(struct at91_twi_dev *dev) 


static void at91_twi_read_next_byte(struct at91_twi_dev *dev)

{

	if (!dev->buf_len)

	/*

	 * If we are in this case, it means there is garbage data in RHR, so

	 * delete them.

	 */

	if (!dev->buf_len) {

		at91_twi_read(dev, AT91_TWI_RHR);

		return;

	}



	/* 8bit read works with and without FIFO */

	*dev->buf = readb_relaxed(dev->base + AT91_TWI_RHR);
@@ -465,6 +471,24 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) 


	if (!irqstatus)

		return IRQ_NONE;

	/*

	 * In reception, the behavior of the twi device (before sama5d2) is

	 * weird. There is some magic about RXRDY flag! When a data has been

	 * almost received, the reception of a new one is anticipated if there

	 * is no stop command to send. That is the reason why ask for sending

	 * the stop command not on the last data but on the second last one.

	 *

	 * Unfortunately, we could still have the RXRDY flag set even if the

	 * transfer is done and we have read the last data. It might happen

	 * when the i2c slave device sends too quickly data after receiving the

	 * ack from the master. The data has been almost received before having

	 * the order to send stop. In this case, sending the stop command could

	 * cause a RXRDY interrupt with a TXCOMP one. It is better to manage

	 * the RXRDY interrupt first in order to not keep garbage data in the

	 * Receive Holding Register for the next transfer.

	 */

	if (irqstatus & AT91_TWI_RXRDY)

		at91_twi_read_next_byte(dev);



	/*

	 * When a NACK condition is detected, the I2C controller sets the NACK,
@@ -507,8 +531,6 @@ static irqreturn_t atmel_twi_interrupt(int irq, void *dev_id) 
	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);

	}
@@ -525,7 +547,6 @@ 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
@@ -577,7 +598,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev) 
	dev->transfer_status = 0;



	/* Clear pending interrupts, such as NACK. */

	sr = at91_twi_read(dev, AT91_TWI_SR);

	at91_twi_read(dev, AT91_TWI_SR);



	if (dev->fifo_size) {

		unsigned fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);
@@ -600,11 +621,6 @@ 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 (sr & AT91_TWI_RXRDY) {

			dev_err(dev->dev, "RXRDY still set!");

			at91_twi_read(dev, AT91_TWI_RHR);

		}



		/* if only one byte is to be read, immediately stop transfer */

		if (!has_alt_cmd && dev->buf_len <= 1 &&

		    !(dev->msg->flags & I2C_M_RECV_LEN))