soc: qcom: aoss: Read back before triggering the IRQ

In some device memory used by msm_qmp, there can be an early ack of a
write to memory succeeding. This may cause the outgoing interrupt to be
triggered before the msgram reflects the write.

Add a readback to ensure the data is flushed to device memory before
triggering the ipc interrupt.
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>
Link: https://lore.kernel.org/r/1579681454-1229-1-git-send-email-aneela@codeaurora.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/soc/qcom/qcom_aoss.c

@@ -225,6 +225,7 @@ static bool qmp_message_empty(struct qmp *qmp)
 static int qmp_send(struct qmp *qmp, const void *data, size_t len)
 {
 	long time_left;
+	size_t tlen;
 	int ret;
 
 	if (WARN_ON(len + sizeof(u32) > qmp->size))
@@ -239,6 +240,9 @@ static int qmp_send(struct qmp *qmp, const void *data, size_t len)
 	__iowrite32_copy(qmp->msgram + qmp->offset + sizeof(u32),
 			 data, len / sizeof(u32));
 	writel(len, qmp->msgram + qmp->offset);
+
+	/* Read back len to confirm data written in message RAM */
+	tlen = readl(qmp->msgram + qmp->offset);
 	qmp_kick(qmp);
 
 	time_left = wait_event_interruptible_timeout(qmp->event,