[PATCH v4 9/9] cxl/mem: Add payload dumping for debug

[Ben Widawsky <ben.widawsky@intel.com>]

It's often useful in debug scenarios to see what the hardware has dumped
out. As it stands today, any device error will result in the payload not
being copied out, so there is no way to triage commands which weren't
expected to fail (and sometimes the payload may have that information).

The functionality is protected by normal kernel security mechanisms as
well as a CONFIG option in the CXL driver.

This was extracted from the original version of the CXL enabling patch
series.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
---
 drivers/cxl/Kconfig | 13 +++++++++++++
 drivers/cxl/mem.c   |  8 ++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 97dc4d751651..3eec9276e586 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -50,4 +50,17 @@ config CXL_MEM_RAW_COMMANDS
 	  potential impact to memory currently in use by the kernel.
 
 	  If developing CXL hardware or the driver say Y, otherwise say N.
+
+config CXL_MEM_INSECURE_DEBUG
+	bool "CXL.mem debugging"
+	depends on CXL_MEM
+	help
+	  Enable debug of all CXL command payloads.
+
+	  Some CXL devices and controllers support encryption and other
+	  security features. The payloads for the commands that enable
+	  those features may contain sensitive clear-text security
+	  material. Disable debug of those command payloads by default.
+	  If you are a kernel developer actively working on CXL
+	  security enabling say Y, otherwise say N.
 endif
diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index dc608bb20a31..237b956f0be0 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -342,6 +342,14 @@ static int __cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm,
 
 	/* #5 */
 	rc = cxl_mem_wait_for_doorbell(cxlm);
+
+	if (!cxl_is_security_command(mbox_cmd->opcode) ||
+	    IS_ENABLED(CONFIG_CXL_MEM_INSECURE_DEBUG)) {
+		print_hex_dump_debug("Payload ", DUMP_PREFIX_OFFSET, 16, 1,
+				     mbox_cmd->payload_in, mbox_cmd->size_in,
+				     true);
+	}
+
 	if (rc == -ETIMEDOUT) {
 		cxl_mem_mbox_timeout(cxlm, mbox_cmd);
 		return rc;
-- 
2.30.1