linux-kernel - [PATCH 5.15 138/913] mailbox: tegra-hsp: Flush whole channel

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Date:   Tue,  5 Apr 2022 09:20:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Pekka Pessi <ppessi@...dia.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: [PATCH 5.15 138/913] mailbox: tegra-hsp: Flush whole channel

From: Pekka Pessi <ppessi@...dia.com>

commit 60de2d2dc284e0dd1c2c897d08625bde24ef3454 upstream.

The txdone can re-fill the mailbox. Keep polling the mailbox during the
flush until all the messages have been delivered.

This fixes an issue with the Tegra Combined UART (TCU) where output can
get truncated under high traffic load.

Signed-off-by: Pekka Pessi <ppessi@...dia.com>
Tested-by: Jon Hunter <jonathanh@...dia.com>
Fixes: 91b1b1c3da8a ("mailbox: tegra-hsp: Add support for shared mailboxes")
Cc: stable@...r.kernel.org
Signed-off-by: Thierry Reding <treding@...dia.com>
Reviewed-by: Jon Hunter <jonathanh@...dia.com>
Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/mailbox/tegra-hsp.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/mailbox/tegra-hsp.c
+++ b/drivers/mailbox/tegra-hsp.c
@@ -412,6 +412,11 @@ static int tegra_hsp_mailbox_flush(struc
 		value = tegra_hsp_channel_readl(ch, HSP_SM_SHRD_MBOX);
 		if ((value & HSP_SM_SHRD_MBOX_FULL) == 0) {
 			mbox_chan_txdone(chan, 0);
+
+			/* Wait until channel is empty */
+			if (chan->active_req != NULL)
+				continue;
+
 			return 0;
 		}