[PATCH v2 3/3] mctp i3c: Clamp transfer lengths to the controller limits

[Shubham Patil <shubhamsanjay.patil@amd.com>]

mctp_i3c_setup() takes the maximum read and write lengths straight from
GETMRL and GETMWL. Those describe the endpoint alone, so on a controller
with a smaller limit every read can be built too large and rejected.
Transmit packets can similarly reach the controller even when they are
larger than its transmit buffer. The receive path also allocates an skb
for data the hardware can never deliver.

Use i3c_device_get_max_read_xfer_bytes() and
i3c_device_get_max_write_xfer_bytes() instead, which return the smaller
of the endpoint and controller limits.

Behaviour is unchanged when neither reports a limit, as the helpers
return 0 exactly as the GETMRL and GETMWL fields do today.

Signed-off-by: Shubham Patil <shubhamsanjay.patil@amd.com>
---
 drivers/net/mctp/mctp-i3c.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/mctp/mctp-i3c.c b/drivers/net/mctp/mctp-i3c.c
index 88d9e36cd4a2..6d08898e1d21 100644
--- a/drivers/net/mctp/mctp-i3c.c
+++ b/drivers/net/mctp/mctp-i3c.c
@@ -81,9 +81,9 @@ struct mctp_i3c_device {
 	bool have_mdb;
 	/* I3C dynamic address */
 	u8 addr;
-	/* Maximum read length */
+	/* Maximum read length, limited by the device MRL and the controller */
 	u16 mrl;
-	/* Maximum write length */
+	/* Maximum write length, limited by the device MWL and the controller */
 	u16 mwl;
 	/* Provisioned ID */
 	u64 pid;
@@ -214,8 +214,8 @@ static int mctp_i3c_setup(struct mctp_i3c_device *mi)
 	i3c_device_get_info(mi->i3c, &info);
 	mi->have_mdb = info.bcr & BIT(2);
 	mi->addr = info.dyn_addr;
-	mi->mwl = info.max_write_len;
-	mi->mrl = info.max_read_len;
+	mi->mwl = i3c_device_get_max_write_xfer_bytes(mi->i3c);
+	mi->mrl = i3c_device_get_max_read_xfer_bytes(mi->i3c);
 	mi->pid = info.pid;
 
 	rc = i3c_device_request_ibi(mi->i3c, &ibi);
-- 
2.34.1