[PATCH 2/4] MIPS: sgi-ip32: Leave MACE PCI control alone in config accesses

[Imre Kaloz]

mace_pci_read_config() clears the master abort interrupt enable in the
MACE PCI control register around each config read. A register read
followed by two register writes can hang CRIME 1.1 under DMA load.

Ack master aborts in the error register instead, and follow every
write with a read so back-to-back accesses cannot form that sequence.

Fixes: c990081bf87b ("[MIPS] Fix IP32 breakage")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Imre Kaloz <kaloz@xxxxxxxxxx>
---
 arch/mips/pci/ops-mace.c | 26 +++++++++++++++++++-------
 arch/mips/pci/pci-ip32.c |  2 ++
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/arch/mips/pci/ops-mace.c b/arch/mips/pci/ops-mace.c
index 951d8070fb48..8827e5f2ea46 100644
--- a/arch/mips/pci/ops-mace.c
+++ b/arch/mips/pci/ops-mace.c
@@ -35,15 +35,27 @@ static inline int mkaddr(struct pci_bus *bus, unsigned int devfn,
 		(reg & 0xfc);
 }
 
+/*
+ * On CRIME 1.1, a MACE PCI register read followed by two register writes
+ * can hang the machine under DMA load, so every register write in this
+ * file is followed by a read.  Config cycles to empty slots end in a
+ * master abort; ack it with interrupts still off so the bridge error
+ * interrupt does not report it.
+ */
+static void mace_pci_ack_abort(void)
+{
+	u32 error = mace->pci.error;
+
+	if (error & MACEPCI_ERROR_MASTER_ABORT) {
+		mace->pci.error = error & ~MACEPCI_ERROR_MASTER_ABORT;
+		mace->pci.error;
+	}
+}
 
 static int
 mace_pci_read_config(struct pci_bus *bus, unsigned int devfn,
 		     int reg, int size, u32 *val)
 {
-	u32 control = mace->pci.control;
-
-	/* disable master aborts interrupts during config read */
-	mace->pci.control = control & ~MACEPCI_CONTROL_MAR_INT;
 	mace->pci.config_addr = mkaddr(bus, devfn, reg);
 	switch (size) {
 	case 1:
@@ -56,9 +68,7 @@ mace_pci_read_config(struct pci_bus *bus, unsigned int devfn,
 		*val = mace->pci.config_data.l;
 		break;
 	}
-	/* ack possible master abort */
-	mace->pci.error &= ~MACEPCI_ERROR_MASTER_ABORT;
-	mace->pci.control = control;
+	mace_pci_ack_abort();
 	/*
 	 * someone forgot to set the ultra bit for the onboard
 	 * scsi chips; we fake it here
@@ -77,6 +87,7 @@ mace_pci_write_config(struct pci_bus *bus, unsigned int devfn,
 		      int reg, int size, u32 val)
 {
 	mace->pci.config_addr = mkaddr(bus, devfn, reg);
+	mace->pci.error;
 	switch (size) {
 	case 1:
 		mace->pci.config_data.b[(reg & 3) ^ 3] = val;
@@ -88,6 +99,7 @@ mace_pci_write_config(struct pci_bus *bus, unsigned int devfn,
 		mace->pci.config_data.l = val;
 		break;
 	}
+	mace_pci_ack_abort();
 
 	DPRINTK("write%d: reg=%08x,val=%02x\n", size * 8, reg, val);
 
diff --git a/arch/mips/pci/pci-ip32.c b/arch/mips/pci/pci-ip32.c
index 30aca6f76563..41ec8453c865 100644
--- a/arch/mips/pci/pci-ip32.c
+++ b/arch/mips/pci/pci-ip32.c
@@ -77,6 +77,8 @@ static irqreturn_t macepci_error(int irq, void *dev)
 	}
 
 	mace->pci.error = flags;
+	/* follow the write with a read, see mace_pci_ack_abort() */
+	mace->pci.error;
 
 	return IRQ_HANDLED;
 }
-- 
2.47.3