linux-kernel - [PATCH 1/4] m68k/mac: Don't send IOP message until channel is idle

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Message-Id: <6d667c39e53865661fa5a48f16829d18ed8abe54.1590880333.git.fthain@telegraphics.com.au>
Date:   Sun, 31 May 2020 09:12:13 +1000
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Joshua Thompson <funaho@...ai.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] m68k/mac: Don't send IOP message until channel is idle

In the following sequence of calls, iop_do_send() gets called when the
"send" channel is not in the IOP_MSG_IDLE state:

iop_ism_irq()
        iop_handle_send()
                (msg->handler)()
                        iop_send_message()
                iop_do_send()

Avoid this by testing the channel state before calling iop_do_send().

When sending, and iop_send_queue is empty, call iop_do_send() because
the channel is idle. If iop_send_queue is not empty, iop_do_send() will
get called later by iop_handle_send().

Cc: Joshua Thompson <funaho@...ai.org>
Tested-by: Stan Johnson <userm57@...oo.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
---
 arch/m68k/mac/iop.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/m68k/mac/iop.c b/arch/m68k/mac/iop.c
index d99c7ea08d8c..22c4e2b8bdf2 100644
--- a/arch/m68k/mac/iop.c
+++ b/arch/m68k/mac/iop.c
@@ -415,7 +415,8 @@ static void iop_handle_send(uint iop_num, uint chan)
 	msg->status = IOP_MSGSTATUS_UNUSED;
 	msg = msg->next;
 	iop_send_queue[iop_num][chan] = msg;
-	if (msg) iop_do_send(msg);
+	if (msg && iop_readb(iop, IOP_ADDR_SEND_STATE + chan) == IOP_MSG_IDLE)
+		iop_do_send(msg);
 }
 
 /*
@@ -489,16 +490,12 @@ int iop_send_message(uint iop_num, uint chan, void *privdata,
 
 	if (!(q = iop_send_queue[iop_num][chan])) {
 		iop_send_queue[iop_num][chan] = msg;
+		iop_do_send(msg);
 	} else {
 		while (q->next) q = q->next;
 		q->next = msg;
 	}
 
-	if (iop_readb(iop_base[iop_num],
-	    IOP_ADDR_SEND_STATE + chan) == IOP_MSG_IDLE) {
-		iop_do_send(msg);
-	}
-
 	return 0;
 }
 
-- 
2.26.2