nvme-apple: reset controller during shutdown

This is a functional revert of c76b8308 ("nvme-apple: fix controller
shutdown in apple_nvme_disable").

The commit broke suspend/resume since apple_nvme_reset_work() tries to
disable the controller on resume. This does not work for the apple NVMe
controller since register access only works while the co-processor
firmware is running.

Disabling the NVMe controller in the shutdown path is also required
for shutting the co-processor down. The original code was appropriate
for this hardware. Add a comment to prevent a similar breaking changes
in the future.

Fixes: c76b8308 ("nvme-apple: fix controller shutdown in apple_nvme_disable")
Reported-by: Janne Grunau <j@jannau.net>
Link: https://lore.kernel.org/all/20230110174745.GA3576@jannau.net/Signed-off-by: Janne Grunau <j@jannau.net>
[hch: updated with a more descriptive comment from Hector Martin]
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/apple.c

@@ -829,7 +829,23 @@ static void apple_nvme_disable(struct apple_nvme *anv, bool shutdown)
 			apple_nvme_remove_cq(anv);
 		}
 
-		nvme_disable_ctrl(&anv->ctrl, shutdown);
+		/*
+		 * Always disable the NVMe controller after shutdown.
+		 * We need to do this to bring it back up later anyway, and we
+		 * can't do it while the firmware is not running (e.g. in the
+		 * resume reset path before RTKit is initialized), so for Apple
+		 * controllers it makes sense to unconditionally do it here.
+		 * Additionally, this sequence of events is reliable, while
+		 * others (like disabling after bringing back the firmware on
+		 * resume) seem to run into trouble under some circumstances.
+		 *
+		 * Both U-Boot and m1n1 also use this convention (i.e. an ANS
+		 * NVMe controller is handed off with firmware shut down, in an
+		 * NVMe disabled state, after a clean shutdown).
+		 */
+		if (shutdown)
+			nvme_disable_ctrl(&anv->ctrl, shutdown);
+		nvme_disable_ctrl(&anv->ctrl, false);
 	}
 
 	WRITE_ONCE(anv->ioq.enabled, false);