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* [PATCH] m68k/mac: Avoid stuck ISM IOP interrupt on Quadra 900/950
@ 2020-05-20  4:32 Finn Thain
  2020-05-25  8:46 ` Geert Uytterhoeven
  0 siblings, 1 reply; 2+ messages in thread
From: Finn Thain @ 2020-05-20  4:32 UTC (permalink / raw)
  To: Geert Uytterhoeven; +Cc: Joshua Thompson, linux-m68k, linux-kernel

On a Quadra 900/950, the ISM IOP IRQ output pin is connected to an
edge-triggered input on VIA2. It is theoretically possible that this
signal could fail to produce the expected VIA2 interrupt.

The two IOP interrupt flags can be asserted in any order but the logic
in iop_ism_irq() does not allow for that. In particular, INT0 can be
asserted right after INT0 is checked and before INT1 is cleared.

Such an interrupt would produce no new edge and VIA2 would detect no
further interrupts from the IOP. Avoid this by looping over the INT0/1
handlers so an edge can be produced.

Cc: Joshua Thompson <funaho@jurai.org>
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
---
 arch/m68k/mac/iop.c | 50 +++++++++++++++++++++++++--------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/arch/m68k/mac/iop.c b/arch/m68k/mac/iop.c
index 9bfa17015768..100e5112fd9e 100644
--- a/arch/m68k/mac/iop.c
+++ b/arch/m68k/mac/iop.c
@@ -566,36 +566,42 @@ irqreturn_t iop_ism_irq(int irq, void *dev_id)
 	uint iop_num = (uint) dev_id;
 	volatile struct mac_iop *iop = iop_base[iop_num];
 	int i,state;
+	u8 events = iop->status_ctrl & (IOP_INT0 | IOP_INT1);
 
 	iop_pr_debug("status %02X\n", iop->status_ctrl);
 
-	/* INT0 indicates a state change on an outgoing message channel */
-
-	if (iop->status_ctrl & IOP_INT0) {
-		iop->status_ctrl = IOP_INT0 | IOP_RUN | IOP_AUTOINC;
-		iop_pr_debug("new status %02X, send states", iop->status_ctrl);
-		for (i = 0 ; i < NUM_IOP_CHAN  ; i++) {
-			state = iop_readb(iop, IOP_ADDR_SEND_STATE + i);
-			iop_pr_cont(" %02X", state);
-			if (state == IOP_MSG_COMPLETE) {
-				iop_handle_send(iop_num, i);
+	do {
+		/* INT0 indicates state change on an outgoing message channel */
+		if (events & IOP_INT0) {
+			iop->status_ctrl = IOP_INT0 | IOP_RUN | IOP_AUTOINC;
+			iop_pr_debug("new status %02X, send states",
+			             iop->status_ctrl);
+			for (i = 0; i < NUM_IOP_CHAN; i++) {
+				state = iop_readb(iop, IOP_ADDR_SEND_STATE + i);
+				iop_pr_cont(" %02X", state);
+				if (state == IOP_MSG_COMPLETE)
+					iop_handle_send(iop_num, i);
 			}
+			iop_pr_cont("\n");
 		}
-		iop_pr_cont("\n");
-	}
 
-	if (iop->status_ctrl & IOP_INT1) {	/* INT1 for incoming msgs */
-		iop->status_ctrl = IOP_INT1 | IOP_RUN | IOP_AUTOINC;
-		iop_pr_debug("new status %02X, recv states", iop->status_ctrl);
-		for (i = 0 ; i < NUM_IOP_CHAN ; i++) {
-			state = iop_readb(iop, IOP_ADDR_RECV_STATE + i);
-			iop_pr_cont(" %02X", state);
-			if (state == IOP_MSG_NEW) {
-				iop_handle_recv(iop_num, i);
+		/* INT1 for incoming messages */
+		if (events & IOP_INT1) {
+			iop->status_ctrl = IOP_INT1 | IOP_RUN | IOP_AUTOINC;
+			iop_pr_debug("new status %02X, recv states",
+			             iop->status_ctrl);
+			for (i = 0; i < NUM_IOP_CHAN; i++) {
+				state = iop_readb(iop, IOP_ADDR_RECV_STATE + i);
+				iop_pr_cont(" %02X", state);
+				if (state == IOP_MSG_NEW)
+					iop_handle_recv(iop_num, i);
 			}
+			iop_pr_cont("\n");
 		}
-		iop_pr_cont("\n");
-	}
+
+		events = iop->status_ctrl & (IOP_INT0 | IOP_INT1);
+	} while (events);
+
 	return IRQ_HANDLED;
 }
 
-- 
2.26.2


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] m68k/mac: Avoid stuck ISM IOP interrupt on Quadra 900/950
  2020-05-20  4:32 [PATCH] m68k/mac: Avoid stuck ISM IOP interrupt on Quadra 900/950 Finn Thain
@ 2020-05-25  8:46 ` Geert Uytterhoeven
  0 siblings, 0 replies; 2+ messages in thread
From: Geert Uytterhoeven @ 2020-05-25  8:46 UTC (permalink / raw)
  To: Finn Thain; +Cc: Joshua Thompson, linux-m68k, Linux Kernel Mailing List

On Wed, May 20, 2020 at 6:41 AM Finn Thain <fthain@telegraphics.com.au> wrote:
> On a Quadra 900/950, the ISM IOP IRQ output pin is connected to an
> edge-triggered input on VIA2. It is theoretically possible that this
> signal could fail to produce the expected VIA2 interrupt.
>
> The two IOP interrupt flags can be asserted in any order but the logic
> in iop_ism_irq() does not allow for that. In particular, INT0 can be
> asserted right after INT0 is checked and before INT1 is cleared.
>
> Such an interrupt would produce no new edge and VIA2 would detect no
> further interrupts from the IOP. Avoid this by looping over the INT0/1
> handlers so an edge can be produced.
>
> Cc: Joshua Thompson <funaho@jurai.org>
> Tested-by: Stan Johnson <userm57@yahoo.com>
> Signed-off-by: Finn Thain <fthain@telegraphics.com.au>

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
i.e. will queue in the m68k for-v5.8 branch.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2020-05-20  4:32 [PATCH] m68k/mac: Avoid stuck ISM IOP interrupt on Quadra 900/950 Finn Thain
2020-05-25  8:46 ` Geert Uytterhoeven

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