netdev - [wpan-next v3 3/3] net: mac802154: Explain the use of ieee802154_wake/stop

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Date:   Tue, 25 Jan 2022 13:25:40 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>
Subject: [wpan-next v3 3/3] net: mac802154: Explain the use of ieee802154_wake/stop_queue()

It is not straightforward to the newcomer that a single skb can
currently be sent at a time and that the internal process is to stop the
queue when processing a frame before re-enabling it.

Make this clear by documenting the ieee802154_wake/stop_queue()
helpers.

Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
---
 include/net/mac802154.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/net/mac802154.h b/include/net/mac802154.h
index d524ffb9eb25..2c3bbc6645ba 100644
--- a/include/net/mac802154.h
+++ b/include/net/mac802154.h
@@ -464,6 +464,12 @@ void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb,
  * ieee802154_wake_queue - wake ieee802154 queue
  * @hw: pointer as obtained from ieee802154_alloc_hw().
  *
+ * Tranceivers usually have either one transmit framebuffer or one framebuffer
+ * for both transmitting and receiving. Hence, the core currently only handles
+ * one frame at a time for each phy, which means we had to stop the queue to
+ * avoid new skb to come during the transmission. The queue then needs to be
+ * woken up after the operation.
+ *
  * Drivers should use this function instead of netif_wake_queue.
  */
 void ieee802154_wake_queue(struct ieee802154_hw *hw);
@@ -472,6 +478,12 @@ void ieee802154_wake_queue(struct ieee802154_hw *hw);
  * ieee802154_stop_queue - stop ieee802154 queue
  * @hw: pointer as obtained from ieee802154_alloc_hw().
  *
+ * Tranceivers usually have either one transmit framebuffer or one framebuffer
+ * for both transmitting and receiving. Hence, the core currently only handles
+ * one frame at a time for each phy, which means we need to tell upper layers to
+ * stop giving us new skbs while we are busy with the transmitted one. The queue
+ * must then be stopped before transmitting.
+ *
  * Drivers should use this function instead of netif_stop_queue.
  */
 void ieee802154_stop_queue(struct ieee802154_hw *hw);
-- 
2.27.0