On Thu, Sep 17, 2020 at 10:57:04PM +0200, Wolfram Sang wrote:

On Wed, Sep 16, 2020 at 10:22:55PM -0700, Sultan Alsawaf wrote:

quoted

From: Sultan Alsawaf <redacted>

According to the SMBus 3.0 protocol specification, block transfer limits
were increased from 32 bytes to 255 bytes. Remove the obsolete 32-byte
limitation.

Sadly, it is not that easy. We are trying to extend BLOCK_MAX to 255
(SMBus 3 specs) but there are various things to be considered,
especially with buffers and when passing it to userspace. Check here for
the discussion (and you are welcome to join, of course):

http://patchwork.ozlabs.org/project/linux-i2c/list/?submitter=79741&state=*

quoted

Signed-off-by: Sultan Alsawaf <redacted>
---
 drivers/i2c/busses/i2c-designware-master.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index 22f28516bca7..5bd64bd17d94 100644
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c

@@ -433,7 +433,7 @@ i2c_dw_read(struct dw_i2c_dev *dev)
 			regmap_read(dev->map, DW_IC_DATA_CMD, &tmp);
 			if (flags & I2C_M_RECV_LEN) {
 				/* Ensure length byte is a valid value */
-				if (tmp <= I2C_SMBUS_BLOCK_MAX && tmp > 0)
+				if (tmp > 0)
 					len = i2c_dw_recv_len(dev, tmp);
 				else
 					len = i2c_dw_recv_len(dev, len);

-- 
2.28.0

Yes, it is not that easy to make the change on a global scale. However, in the
case of the designware adapter, it really *is* that easy. This change covers the
designware adapter, and others can follow later with the much more invasive
changes that are needed.

Sultan