drm/amd/display: Add hardware reset interface for DMUB service

[Why]
We'll need this to perform a clean shutdown before unloading the driver.

[How]
It will call reset internally and set hw_init to false. It won't do
anything if the hardware isn't initialized.

Signed-off-by: Nicholas Kazlauskas <[e-mail]>
Reviewed-by: Tony Cheng <[e-mail]>
Acked-by: Bhawanpreet Lakha <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dmub/inc/dmub_srv.h

···
 				  const struct dmub_srv_hw_params *params);
 
 /**
+ * dmub_srv_hw_reset() - puts the DMUB hardware in reset state if initialized
+ * @dmub: the dmub service
+ *
+ * Before destroying the DMUB service or releasing the backing framebuffer
+ * memory we'll need to put the DMCUB into reset first.
+ *
+ * A subsequent call to dmub_srv_hw_init() will re-enable the DMCUB.
+ *
+ * Return:
+ *   DMUB_STATUS_OK - success
+ *   DMUB_STATUS_INVALID - unspecified error
+ */
+enum dmub_status dmub_srv_hw_reset(struct dmub_srv *dmub);
+
+/**
  * dmub_srv_cmd_queue() - queues a command to the DMUB
  * @dmub: the dmub service
  * @cmd: the command to queue

drivers/gpu/drm/amd/display/dmub/src/dmub_srv.c

···
 	return DMUB_STATUS_OK;
 }
 
+enum dmub_status dmub_srv_hw_reset(struct dmub_srv *dmub)
+{
+	if (!dmub->sw_init)
+		return DMUB_STATUS_INVALID;
+
+	if (dmub->hw_init == false)
+		return DMUB_STATUS_OK;
+
+	if (dmub->hw_funcs.reset)
+		dmub->hw_funcs.reset(dmub);
+
+	dmub->hw_init = false;
+
+	return DMUB_STATUS_OK;
+}
+
 enum dmub_status dmub_srv_cmd_queue(struct dmub_srv *dmub,
 				    const struct dmub_cmd_header *cmd)
 {