[RFC PATCH 2/2] rtsx_usb: avoid USB I/O in runtime autosuspend

[Sean Rhodes <sean@starlabs.systems>]

The runtime autosuspend callback currently queries card status and clears
OCP via USB register accesses.

On some systems this can deadlock runtime PM and leave the USB device
stuck in the "suspending" state.

Avoid issuing USB commands from the runtime autosuspend callback.
Instead, use the last cached card status (updated on successful status
reads) and conservatively assume a card may be present until status is
known.

Signed-off-by: Sean Rhodes <sean@starlabs.systems>
---
 drivers/misc/cardreader/rtsx_usb.c | 11 +++++++----
 include/linux/rtsx_usb.h           |  3 +++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/cardreader/rtsx_usb.c b/drivers/misc/cardreader/rtsx_usb.c
index c8badd0db87b..727205e84640 100644
--- a/drivers/misc/cardreader/rtsx_usb.c
+++ b/drivers/misc/cardreader/rtsx_usb.c
@@ -336,6 +336,9 @@ int rtsx_usb_get_card_status(struct rtsx_ucr *ucr, u16 *status)
 	if (ret < 0)
 		return ret;
 
+	ucr->card_status_cache = *status;
+	ucr->card_status_valid = true;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(rtsx_usb_get_card_status);
@@ -753,16 +756,16 @@ static int rtsx_usb_suspend(struct usb_interface *intf, pm_message_t message)
 
 	if (PMSG_IS_AUTO(message)) {
 		if (mutex_trylock(&ucr->dev_mutex)) {
-			rtsx_usb_get_card_status(ucr, &val);
+			if (ucr->card_status_valid)
+				val = ucr->card_status_cache;
+			else
+				val = SD_CD | MS_CD;
 			mutex_unlock(&ucr->dev_mutex);
 
 			/* Defer the autosuspend if card exists */
 			if (val & (SD_CD | MS_CD)) {
 				device_for_each_child(&intf->dev, NULL, rtsx_usb_resume_child);
 				return -EAGAIN;
-			} else {
-				/* if the card does not exists, clear OCP status */
-				rtsx_usb_write_register(ucr, OCPCTL, MS_OCP_CLEAR, MS_OCP_CLEAR);
 			}
 		} else {
 			/* There is an ongoing operation*/
diff --git a/include/linux/rtsx_usb.h b/include/linux/rtsx_usb.h
index 54c6ea82bf43..fed695760691 100644
--- a/include/linux/rtsx_usb.h
+++ b/include/linux/rtsx_usb.h
@@ -62,6 +62,9 @@ struct rtsx_ucr {
 	struct usb_interface	*pusb_intf;
 	struct usb_sg_request	current_sg;
 
+	u16			card_status_cache;
+	bool			card_status_valid;
+
 	struct timer_list	sg_timer;
 	struct mutex		dev_mutex;
 };