[RFC PATCH] powerpc/pseries/msi: Avoid reading PCI device registers in reduced power state

[Gautam Menghani <gautam@linux.ibm.com>]

When a system is being suspended to RAM, the PCI devices are also
suspended and the code ends up calling pseries_msi_compose_msg() and this
triggers the BUG_ON() in __pci_read_msi_msg() because the device at that
point is in reduced power state. In reduced power state, the memory
mapped registers of the device are not accessible.

To replicate the bug:
1. Make sure deep sleep is selected
	# cat /sys/power/mem_sleep
	s2idle [deep]

2. Suspend the system
	echo mem > /sys/power/state

To fix this behaviour, read the cached msi message of the device when the
device is not in PCI_D0 power state instead of touching the hardware.

Fixes: a5f3d2c17b07 ("powerpc/pseries/pci: Add MSI domains")
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
---
 arch/powerpc/platforms/pseries/msi.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/msi.c b/arch/powerpc/platforms/pseries/msi.c
index fdc2f7f38dc9..458d95c8c755 100644
--- a/arch/powerpc/platforms/pseries/msi.c
+++ b/arch/powerpc/platforms/pseries/msi.c
@@ -525,7 +525,12 @@ static struct msi_domain_info pseries_msi_domain_info = {
 
 static void pseries_msi_compose_msg(struct irq_data *data, struct msi_msg *msg)
 {
-	__pci_read_msi_msg(irq_data_get_msi_desc(data), msg);
+	struct pci_dev *dev = msi_desc_to_pci_dev(irq_data_get_msi_desc(data));
+
+	if (dev->current_state == PCI_D0)
+		__pci_read_msi_msg(irq_data_get_msi_desc(data), msg);
+	else
+		get_cached_msi_msg(data->irq, msg);
 }
 
 static struct irq_chip pseries_msi_irq_chip = {
-- 
2.47.0