cxl: Do adapter fence check before handling afu interrupt

If an afu interrupt is in flight when an eeh error is triggered the
control still reaches the function native_irq_multiplexed and the
PE-Handle read from the CXL_PSL_PEHandle_An register is 0xffff. The
function then erroneously assumes that the interrupt belonged to a
detached context and generates a warning with full stack dump in the
kernel log complaining:

"Unable to demultiplex CXL PSL IRQ for PE 65535 DSISR ffffffff DAR
ffffffff. (Possible AFU HW issue - was a term/remove acked with
outstanding transactions"

To fix this the patch adds new code to the function
native_irq_multiplexed function to compares the read value of register
CXL_PSL_PEHandle_An to ~0ULL. If true then logs a warning message
saying that the interrupt is being ignored and returns IRQ_HANDLED from
the irq handler.
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/native.c

@@ -931,9 +931,18 @@ static irqreturn_t native_irq_multiplexed(int irq, void *data)
 	struct cxl_afu *afu = data;
 	struct cxl_context *ctx;
 	struct cxl_irq_info irq_info;
-	int ph = cxl_p2n_read(afu, CXL_PSL_PEHandle_An) & 0xffff;
-	int ret;
-
+	u64 phreg = cxl_p2n_read(afu, CXL_PSL_PEHandle_An);
+	int ph, ret;
+
+	/* check if eeh kicked in while the interrupt was in flight */
+	if (unlikely(phreg == ~0ULL)) {
+		dev_warn(&afu->dev,
+			 "Ignoring slice interrupt(%d) due to fenced card",
+			 irq);
+		return IRQ_HANDLED;
+	}
+	/* Mask the pe-handle from register value */
+	ph = phreg & 0xffff;
 	if ((ret = native_get_irq_info(afu, &irq_info))) {
 		WARN(1, "Unable to get CXL IRQ Info: %i\n", ret);
 		return fail_psl_irq(afu, &irq_info);