From: Lars-Peter Clausen lars@metafoo.de
[ Upstream commit 9fdf6d97f03035ad5298e2d1635036c74c2090ed ]
SMBus packet error checking (PEC) is implemented by appending one additional byte of checksum data at the end of the message. This provides additional protection and allows to detect data corruption on the I2C bus.
SMBus block reads support variable length reads. The first byte in the read message is the number of available data bytes.
The combination of PEC and block read is currently not supported by the Cadence I2C driver. * When PEC is enabled the maximum transfer length for block reads increases from 33 to 34 bytes. * The I2C core smbus emulation layer relies on the driver updating the `i2c_msg` `len` field with the number of received bytes. The updated length is used when checking the PEC.
Add support to the Cadence I2C driver for handling SMBus block reads with PEC. To determine the maximum transfer length uses the initial `len` value of the `i2c_msg`. When PEC is enabled this will be 2, when it is disabled it will be 1.
Once a read transfer is done also increment the `len` field by the amount of received data bytes.
This change has been tested with a UCM90320 PMBus power monitor, which requires block reads to access certain data fields, but also has PEC enabled by default.
Fixes: df8eb5691c48 ("i2c: Add driver for Cadence I2C controller") Signed-off-by: Lars-Peter Clausen lars@metafoo.de Tested-by: Shubhrajyoti Datta Shubhrajyoti.datta@amd.com Signed-off-by: Wolfram Sang wsa@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/i2c/busses/i2c-cadence.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c index 8750e444f449..72699fdd5d11 100644 --- a/drivers/i2c/busses/i2c-cadence.c +++ b/drivers/i2c/busses/i2c-cadence.c @@ -348,8 +348,13 @@ static void cdns_i2c_mrecv(struct cdns_i2c *id) ctrl_reg = cdns_i2c_readreg(CDNS_I2C_CR_OFFSET); ctrl_reg |= CDNS_I2C_CR_RW | CDNS_I2C_CR_CLR_FIFO;
+ /* + * Receive up to I2C_SMBUS_BLOCK_MAX data bytes, plus one message length + * byte, plus one checksum byte if PEC is enabled. p_msg->len will be 2 if + * PEC is enabled, otherwise 1. + */ if (id->p_msg->flags & I2C_M_RECV_LEN) - id->recv_count = I2C_SMBUS_BLOCK_MAX + 1; + id->recv_count = I2C_SMBUS_BLOCK_MAX + id->p_msg->len;
id->curr_recv_count = id->recv_count;
@@ -535,6 +540,9 @@ static int cdns_i2c_process_msg(struct cdns_i2c *id, struct i2c_msg *msg, if (id->err_status & CDNS_I2C_IXR_ARB_LOST) return -EAGAIN;
+ if (msg->flags & I2C_M_RECV_LEN) + msg->len += min_t(unsigned int, msg->buf[0], I2C_SMBUS_BLOCK_MAX); + return 0; }