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mailbox: mpfs-mbox: replace unbounded BUSY polling with bounded waits

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The MPFS mailbox driver used unbounded polling loops and treated the
BUSY bit as a fatal condition in several paths. On MPFS, BUSY may be
transiently reasserted even after response data is written, which is
observable in U-Boot’s synchronous, polled execution model.

Replace the unbounded loops with a bounded
regmap_read_poll_timeout()-based helper that waits for the controller to
become idle.

This preserves existing behaviour while preventing infinite stalls
and avoiding spurious failures during early boot.

Signed-off-by: Jamie Gibbons <jamie.gibbons@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
This commit is contained in:
Jamie Gibbons
2026-08-05 10:16:07 -07:00
committed by Leo Yu-Chi Liang
parent 899cbeee1c
commit 47cd1fd361
1 changed files with 14 additions and 6 deletions
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drivers/mailbox/mpfs-mbox.c
+14 -6
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@@ -18,6 +18,7 @@
#include <linux/compat.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/iopoll.h>
#include <log.h>
#include <mailbox-uclass.h>
#include <mpfs-mailbox.h>
@@ -60,6 +61,7 @@ static int mpfs_mbox_send(struct mbox_chan *chan, const void *data)
u32 mailbox_val, cmd_shifted, value;
u8 *byte_buf;
u8 idx, byte_idx, byte_offset;
int ret;
u32 *word_buf = (u32 *)msg->cmd_data;
@@ -86,13 +88,19 @@ static int mpfs_mbox_send(struct mbox_chan *chan, const void *data)
regmap_write(mbox->control_scb, SERVICES_CR_OFFSET, cmd_shifted);
do {
regmap_read(mbox->control_scb, SERVICES_CR_OFFSET, &value);
} while (SERVICE_CR_REQ_MASK == (value & SERVICE_CR_REQ_MASK));
ret = regmap_read_poll_timeout(mbox->control_scb, SERVICES_CR_OFFSET,
value, !(value & SERVICE_CR_REQ_MASK),
1, /* poll every 1 µs */
20); /* timeout 20 ms */
if (ret)
return ret;
do {
regmap_read(mbox->control_scb, SERVICES_SR_OFFSET, &value);
} while (SERVICE_SR_BUSY_MASK == (value & SERVICE_SR_BUSY_MASK));
ret = regmap_read_poll_timeout(mbox->control_scb, SERVICES_SR_OFFSET,
value, !(value & SERVICE_SR_BUSY_MASK),
1,
20);
if (ret)
return ret;
msg->response->resp_status = (value >> SERVICE_SR_STATUS_SHIFT);
if (msg->response->resp_status)