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[1/2] i2c: designware: Only check the first byte for SMBus block read length

Message ID 20200614210255.4641-2-sultan@kerneltoast.com
State New
Headers show
Series i2c-hid: Save power by reducing i2c xfers with block reads | expand

Commit Message

Sultan Alsawaf (unemployed) June 14, 2020, 9:02 p.m. UTC 
From: Sultan Alsawaf <sultan@kerneltoast.com>

SMBus block reads can be broken because the read function will just skip
over bytes it doesn't like until reaching a byte that conforms to the
length restrictions for block reads. This is problematic when it isn't
known if the incoming payload is indeed a conforming block read.

According to the SMBus specification, block reads will only send the
payload length in the first byte, so we can fix this by only considering
the first byte in a sequence for block read length purposes.

Fixes: c3ae106050b9 ("i2c: designware: Implement support for SMBus block read and write")
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
---
 drivers/i2c/busses/i2c-designware-master.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
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Patch

diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index d6425ad6e6a3..16d38b8fc19a 100644
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -398,7 +398,6 @@  i2c_dw_recv_len(struct dw_i2c_dev *dev, u8 len)
 	len += (flags & I2C_CLIENT_PEC) ? 2 : 1;
 	dev->tx_buf_len = len - min_t(u8, len, dev->rx_outstanding);
 	msgs[dev->msg_read_idx].len = len;
-	msgs[dev->msg_read_idx].flags &= ~I2C_M_RECV_LEN;
 
 	return len;
 }
@@ -430,10 +429,11 @@  i2c_dw_read(struct dw_i2c_dev *dev)
 			u32 flags = msgs[dev->msg_read_idx].flags;
 
 			regmap_read(dev->map, DW_IC_DATA_CMD, &tmp);
-			/* Ensure length byte is a valid value */
-			if (flags & I2C_M_RECV_LEN &&
-			    tmp <= I2C_SMBUS_BLOCK_MAX && tmp > 0) {
-				len = i2c_dw_recv_len(dev, tmp);
+			if (flags & I2C_M_RECV_LEN) {
+				/* Ensure length byte is a valid value */
+				if (tmp <= I2C_SMBUS_BLOCK_MAX && tmp > 0)
+					len = i2c_dw_recv_len(dev, tmp);
+				msgs[dev->msg_read_idx].flags &= ~I2C_M_RECV_LEN;
 			}
 			*buf++ = tmp;
 			dev->rx_outstanding--;