On 20-12-08 16:24:11, Ben Widawsky wrote:

[snip]

+static int cxl_mem_mbox_send_cmd(struct cxl_mem *cxlm,
+				 struct mbox_cmd *mbox_cmd)
+{
+	u64 cmd, status;
+	size_t out_len;
+	int rc;
+
+	lockdep_assert_held(&cxlm->mbox_lock);
+
+	/*
+	 * Here are the steps from 8.2.8.4 of the CXL 2.0 spec.
+	 *   1. Caller reads MB Control Register to verify doorbell is clear
+	 *   2. Caller writes Command Register
+	 *   3. Caller writes Command Payload Registers if input payload is non-empty
+	 *   4. Caller writes MB Control Register to set doorbell
+	 *   5. Caller either polls for doorbell to be clear or waits for interrupt if configured
+	 *   6. Caller reads MB Status Register to fetch Return code
+	 *   7. If command successful, Caller reads Command Register to get Payload Length
+	 *   8. If output payload is non-empty, host reads Command Payload Registers
+	 */
+
+	/* #1 */
+	WARN_ON(cxl_doorbell_busy(cxlm));
+
+	/* #2 */
+	cxl_write_mbox_reg64(cxlm, CXLDEV_MB_CMD_OFFSET, mbox_cmd->opcode);
+
+	if (mbox_cmd->size_in) {
+		/* #3 */
+		CXL_SET_FIELD(mbox_cmd->size_in, CXLDEV_MB_CMD_PAYLOAD_LENGTH);
+		cxl_mbox_payload_fill(cxlm, mbox_cmd->payload,
+				      mbox_cmd->size_in);
+	}

There is a bug here where the payload length isn't written on input. It was
working in v1. It will be fixed in v3.

[snip]