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i2c: at91: manage unexpected RXRDY flag when starting a transfer

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commit a9bed6b10bd117a300cceb9062003f7a2761ef99 upstream.

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: Peter Rosin <peda@lysator.liu.se>
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Tested-by: Peter Rosin <peda@lysator.liu.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Fixes: 93563a6a71bb ("i2c: at91: fix a race condition when using the DMA controller")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Ludovic Desroches
2015-10-26 10:38:27 +01:00
committed by Willy Tarreau
parent d106ce33dc
commit 98dcb81b30
1 changed files with 26 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files
drivers/i2c/busses/i2c-at91.c
+26 -10
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@@ -273,8 +273,14 @@ error:
static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
{
if (dev->buf_len <= 0)
/*
* 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;
}
*dev->buf = at91_twi_read(dev, AT91_TWI_RHR) & 0xff;
--dev->buf_len;
@@ -371,6 +377,24 @@ 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,
@@ -413,8 +437,6 @@ 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);
}
@@ -429,7 +451,6 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
{
int ret;
bool has_unre_flag = dev->pdata->has_unre_flag;
unsigned sr;
/*
* WARNING: the TXCOMP bit in the Status Register is NOT a clear on
@@ -466,7 +487,7 @@ 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->buf_len) {
at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_QUICK);
@@ -474,11 +495,6 @@ 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 (dev->buf_len <= 1 && !(dev->msg->flags & I2C_M_RECV_LEN))
start_flags |= AT91_TWI_STOP;