On Thu, 5 May 2016 14:22:06 +0100
Jon Hunter [off-list ref] wrote:

Hi Marc,

On 05/05/16 13:06, Marc Zyngier wrote:

quoted

Hi Jon,

On 04/05/16 17:25, Jon Hunter wrote:

quoted

Setting the interrupt type for private peripheral interrupts (PPIs) may
not be supported by a given GIC because it is IMPLEMENTATION DEFINED
whether this is allowed. There is no way to know if setting the type is
supported for a given GIC and so the value written is read back to
verify it matches the desired configuration. If it does not match then
an error is return.

There are cases where the interrupt configuration read from firmware
(such as a device-tree blob), has been incorrect and hence
gic_configure_irq() has returned an error. This error has gone
undetected because the error code returned was ignored but the interrupt
still worked fine because the configuration for the interrupt could not
be overwritten.

Given that this has done undetected and that failing to set the
configuration for a PPI may not be a catastrophic, don't return an error
but WARN if we fail to configure a PPI. This will allows us to fix up
any places in the kernel where we should be checking the return status
and maintain backward compatibility with firmware images that may have
incorrect PPI configurations.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Marc Zyngier <redacted>
---
 drivers/irqchip/irq-gic-common.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/irqchip/irq-gic-common.c b/drivers/irqchip/irq-gic-common.c
index ffff5a45f1e3..9fa92a17225c 100644
--- a/drivers/irqchip/irq-gic-common.c
+++ b/drivers/irqchip/irq-gic-common.c

@@ -56,12 +56,15 @@ int gic_configure_irq(unsigned int irq, unsigned int type,
 
 	/*
 	 * Write back the new configuration, and possibly re-enable
-	 * the interrupt. If we fail to write a new configuration,
-	 * return an error.
+	 * the interrupt. WARN if we fail to write a new configuration
+	 * and return an error if we failed to write the configuration
+	 * for an SPI. If we fail to write the configuration for a PPI
+	 * this is most likely because the GIC does not allow us to set
+	 * the configuration and so it is not a catastrophic failure.
 	 */
 	writel_relaxed(val, base + GIC_DIST_CONFIG + confoff);
-	if (readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val)
-		ret = -EINVAL;
+	if (WARN_ON(readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val))
+		ret = irq < 32 ? 0 : -EINVAL;
 
 	if (sync_access)
 		sync_access();

I'm going to slightly backpedal on that one:

When running in non-secure mode, you can reconfigure secure interrupts

Do you mean 'cannot'?

Yes, sorry.

quoted

(for obvious reasons). But you don't know which mode you're running in
either. A typical example is the arch timer, which requests both secure
and non-secure interrupts, because we cannot know which side of the CPU
we're running on. In the non-secure case, we end-up with a splat that
is rather undeserved.

Yes seems sensible.

quoted

So I'm tempted to tone down the splat in the PPI case like this:

diff --git a/drivers/irqchip/irq-gic-common.c b/drivers/irqchip/irq-gic-common.c
index 083c303..1605e42 100644
--- a/drivers/irqchip/irq-gic-common.c
+++ b/drivers/irqchip/irq-gic-common.c

@@ -63,8 +63,17 @@ int gic_configure_irq(unsigned int irq, unsigned int type,
 	 * the configuration and so it is not a catastrophic failure.
 	 */
 	writel_relaxed(val, base + GIC_DIST_CONFIG + confoff);
-	if (WARN_ON(readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val))
-		ret = irq < 32 ? 0 : -EINVAL;
+	oldval = readl_relaxed(base + GIC_DIST_CONFIG + confoff);
+	if (oldval != val) {
+		if (irq < 32) {
+			pr_warn("GIC: PPI%d is either secure or misconfigured\n",
+				irq - 16);
+			ret = 0;
+		} else {
+			WARN_ON(1);
+			ret = -EINVAL;
+		}
+	}
 
 	if (sync_access)
 		sync_access();

Thoughts?

That is fine with me. Do you want me to re-spin or do you want to apply
your change on top? However, before I re-spin would like to get your
thoughts on patches 13-17.

I can squash this into your own patch if you're OK with it. I'll reply
to your other patches shortly, as I have a number of comments there.

	M.
-- 
Jazz is not dead. It just smells funny.