at91_can.c (0199f866615921ddc5d22fbbab7510e8b403d40c) at91_can.c (88bfb9a713563550b1febb1a89b3a192efe2d091)
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * at91_can.c - CAN network driver for AT91 SoC CAN controller
4 *
5 * (C) 2007 by Hans J. Koch <hjk@hansjkoch.de>
6 * (C) 2008, 2009, 2010, 2011 by Marc Kleine-Budde <kernel@pengutronix.de>
7 */
8

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638 *
639 * Like it or not, but the chip always saves a received CAN message
640 * into the first free mailbox it finds (starting with the
641 * lowest). This makes it very difficult to read the messages in the
642 * right order from the chip. This is how we work around that problem:
643 *
644 * The first message goes into mb nr. 1 and issues an interrupt. All
645 * rx ints are disabled in the interrupt handler and a napi poll is
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * at91_can.c - CAN network driver for AT91 SoC CAN controller
4 *
5 * (C) 2007 by Hans J. Koch <hjk@hansjkoch.de>
6 * (C) 2008, 2009, 2010, 2011 by Marc Kleine-Budde <kernel@pengutronix.de>
7 */
8

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638 *
639 * Like it or not, but the chip always saves a received CAN message
640 * into the first free mailbox it finds (starting with the
641 * lowest). This makes it very difficult to read the messages in the
642 * right order from the chip. This is how we work around that problem:
643 *
644 * The first message goes into mb nr. 1 and issues an interrupt. All
645 * rx ints are disabled in the interrupt handler and a napi poll is
646 * scheduled. We read the mailbox, but do _not_ reenable the mb (to
646 * scheduled. We read the mailbox, but do _not_ re-enable the mb (to
647 * receive another message).
648 *
649 * lower mbxs upper
650 * ____^______ __^__
651 * / \ / \
652 * +-+-+-+-+-+-+-+-++-+-+-+-+
653 * | |x|x|x|x|x|x|x|| | | | |
654 * +-+-+-+-+-+-+-+-++-+-+-+-+
655 * 0 0 0 0 0 0 0 0 0 0 1 1 \ mail
656 * 0 1 2 3 4 5 6 7 8 9 0 1 / box
657 * ^
658 * |
659 * \
660 * unused, due to chip bug
661 *
662 * The variable priv->rx_next points to the next mailbox to read a
663 * message from. As long we're in the lower mailboxes we just read the
647 * receive another message).
648 *
649 * lower mbxs upper
650 * ____^______ __^__
651 * / \ / \
652 * +-+-+-+-+-+-+-+-++-+-+-+-+
653 * | |x|x|x|x|x|x|x|| | | | |
654 * +-+-+-+-+-+-+-+-++-+-+-+-+
655 * 0 0 0 0 0 0 0 0 0 0 1 1 \ mail
656 * 0 1 2 3 4 5 6 7 8 9 0 1 / box
657 * ^
658 * |
659 * \
660 * unused, due to chip bug
661 *
662 * The variable priv->rx_next points to the next mailbox to read a
663 * message from. As long we're in the lower mailboxes we just read the
664 * mailbox but not reenable it.
664 * mailbox but not re-enable it.
665 *
665 *
666 * With completion of the last of the lower mailboxes, we reenable the
666 * With completion of the last of the lower mailboxes, we re-enable the
667 * whole first group, but continue to look for filled mailboxes in the
668 * upper mailboxes. Imagine the second group like overflow mailboxes,
669 * which takes CAN messages if the lower goup is full. While in the
667 * whole first group, but continue to look for filled mailboxes in the
668 * upper mailboxes. Imagine the second group like overflow mailboxes,
669 * which takes CAN messages if the lower goup is full. While in the
670 * upper group we reenable the mailbox right after reading it. Giving
670 * upper group we re-enable the mailbox right after reading it. Giving
671 * the chip more room to store messages.
672 *
673 * After finishing we look again in the lower group if we've still
674 * quota.
675 *
676 */
677static int at91_poll_rx(struct net_device *dev, int quota)
678{

--- 737 unchanged lines hidden --- 		671 * the chip more room to store messages.
672 *
673 * After finishing we look again in the lower group if we've still
674 * quota.
675 *
676 */
677static int at91_poll_rx(struct net_device *dev, int quota)
678{

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