linux-kernel - [PATCH 1/2] mailbox: switch to hrtimer for tx

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Date:	Wed, 22 Jul 2015 13:28:50 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	linux-kernel@...r.kernel.org, Jassi Brar <jassisinghbrar@...il.com>
Cc:	Sudeep Holla <sudeep.holla@....com>,
	Juri Lelli <Juri.Lelli@....com>
Subject: [PATCH 1/2] mailbox: switch to hrtimer for tx_complete polling

After submitting the message via msg_submit in mbox_send_message, we
wait until it has been transmitted and the remote acknowledges it using
some status register which controller can read(i.e. TXDONE_BY_POLL).

However, since the timer used here to handle that polling for the
transmit completion polling is jiffy based, we might end-up waiting
for atleast a jiffy even though the response for that message from the
remote is received via interrupt and processed in relatively smaller
time granularity.

Since some mailbox controller can operate at much lesser granularity
compared to jiffy, switch to the hrtimer in the mailbox core.

Cc: Jassi Brar <jassisinghbrar@...il.com>
Reported-and-suggested-by: Juri Lelli <Juri.Lelli@....com>
Signed-off-by: Sudeep Holla <sudeep.holla@....com>
---
 drivers/mailbox/mailbox.c          | 27 +++++++++++++++------------
 include/linux/mailbox_controller.h |  7 ++++---
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index c7fdb57fd166..6a4811f85705 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -26,8 +26,6 @@
 static LIST_HEAD(mbox_cons);
 static DEFINE_MUTEX(con_mutex);
 
-static void poll_txdone(unsigned long data);
-
 static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
 {
 	int idx;
@@ -88,7 +86,9 @@ static void msg_submit(struct mbox_chan *chan)
 	spin_unlock_irqrestore(&chan->lock, flags);
 
 	if (!err && (chan->txdone_method & TXDONE_BY_POLL))
-		poll_txdone((unsigned long)chan->mbox);
+		/* kick start the timer immediately to avoid delays */
+		hrtimer_start(&chan->mbox->poll_hrt, ktime_set(0, 0),
+			      HRTIMER_MODE_REL);
 }
 
 static void tx_tick(struct mbox_chan *chan, int r)
@@ -112,9 +112,10 @@ static void tx_tick(struct mbox_chan *chan, int r)
 		complete(&chan->tx_complete);
 }
 
-static void poll_txdone(unsigned long data)
+static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer)
 {
-	struct mbox_controller *mbox = (struct mbox_controller *)data;
+	struct mbox_controller *mbox =
+		container_of(hrtimer, struct mbox_controller, poll_hrt);
 	bool txdone, resched = false;
 	int i;
 
@@ -130,9 +131,11 @@ static void poll_txdone(unsigned long data)
 		}
 	}
 
-	if (resched)
-		mod_timer(&mbox->poll, jiffies +
-				msecs_to_jiffies(mbox->txpoll_period));
+	if (resched) {
+		hrtimer_forward_now(hrtimer, ms_to_ktime(mbox->txpoll_period));
+		return HRTIMER_RESTART;
+	}
+	return HRTIMER_NORESTART;
 }
 
 /**
@@ -451,9 +454,9 @@ int mbox_controller_register(struct mbox_controller *mbox)
 		txdone = TXDONE_BY_ACK;
 
 	if (txdone == TXDONE_BY_POLL) {
-		mbox->poll.function = &poll_txdone;
-		mbox->poll.data = (unsigned long)mbox;
-		init_timer(&mbox->poll);
+		hrtimer_init(&mbox->poll_hrt, CLOCK_MONOTONIC,
+			     HRTIMER_MODE_REL);
+		mbox->poll_hrt.function = txdone_hrtimer;
 	}
 
 	for (i = 0; i < mbox->num_chans; i++) {
@@ -495,7 +498,7 @@ void mbox_controller_unregister(struct mbox_controller *mbox)
 		mbox_free_channel(&mbox->chans[i]);
 
 	if (mbox->txdone_poll)
-		del_timer_sync(&mbox->poll);
+		hrtimer_cancel(&mbox->poll_hrt);
 
 	mutex_unlock(&con_mutex);
 }
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index 68c42454439b..74deadb42d76 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -9,7 +9,7 @@
 
 #include <linux/of.h>
 #include <linux/types.h>
-#include <linux/timer.h>
+#include <linux/hrtimer.h>
 #include <linux/device.h>
 #include <linux/completion.h>
 
@@ -67,7 +67,8 @@ struct mbox_chan_ops {
  * @txpoll_period:	If 'txdone_poll' is in effect, the API polls for
  *			last TX's status after these many millisecs
  * @of_xlate:		Controller driver specific mapping of channel via DT
- * @poll:		API private. Used to poll for TXDONE on all channels.
+ * @poll_hrt:		API private. hrtimer used to poll for TXDONE on all
+ *			channels.
  * @node:		API private. To hook into list of controllers.
  */
 struct mbox_controller {
@@ -81,7 +82,7 @@ struct mbox_controller {
 	struct mbox_chan *(*of_xlate)(struct mbox_controller *mbox,
 				      const struct of_phandle_args *sp);
 	/* Internal to API */
-	struct timer_list poll;
+	struct hrtimer poll_hrt;
 	struct list_head node;
 };
 
-- 
1.9.1

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