accel/amdxdna: Fix tail-pointer polling in mailbox_get_msg()

[ Upstream commit cd77d5a ]

In mailbox_get_msg(), mailbox_reg_read_non_zero() is called to poll for a
non-zero tail pointer. This assumed that a zero value indicates an error.
However, certain corner cases legitimately produce a zero tail pointer.
To handle these cases, remove mailbox_reg_read_non_zero(). The zero tail
pointer will be treated as a valid rewind event.

Reviewed-by: Maciej Falkowski <maciej.falkowski@linux.intel.com>
Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Link: https://patch.msgid.link/20251204181603.793824-1-lizhi.hou@amd.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: houlz0507

drivers/accel/amdxdna/amdxdna_mailbox.c

@@ -112,22 +112,6 @@ static u32 mailbox_reg_read(struct mailbox_channel *mb_chann, u32 mbox_reg)
 	return readl(ringbuf_addr);
 }
 
-static int mailbox_reg_read_non_zero(struct mailbox_channel *mb_chann, u32 mbox_reg, u32 *val)
-{
-	struct xdna_mailbox_res *mb_res = &mb_chann->mb->res;
-	void __iomem *ringbuf_addr = mb_res->mbox_base + mbox_reg;
-	int ret, value;
-
-	/* Poll till value is not zero */
-	ret = readx_poll_timeout(readl, ringbuf_addr, value,
-				 value, 1 /* us */, 100);
-	if (ret < 0)
-		return ret;
-
-	*val = value;
-	return 0;
-}
-
 static inline void
 mailbox_set_headptr(struct mailbox_channel *mb_chann, u32 headptr_val)
 {
@@ -288,8 +272,7 @@ static int mailbox_get_msg(struct mailbox_channel *mb_chann)
 	u32 start_addr;
 	int ret;
 
-	if (mailbox_reg_read_non_zero(mb_chann, mb_chann->res[CHAN_RES_I2X].mb_tail_ptr_reg, &tail))
-		return -EINVAL;
+	tail = mailbox_get_tailptr(mb_chann, CHAN_RES_I2X);
 	head = mb_chann->i2x_head;
 	ringbuf_size = mailbox_get_ringbuf_size(mb_chann, CHAN_RES_I2X);
 	start_addr = mb_chann->res[CHAN_RES_I2X].rb_start_addr;