[PATCH V4] PCI/MSI: Fix MSI hwirq truncation

[Vidya Sagar <vidyas@nvidia.com>]

While calculating the hwirq number for an MSI interrupt, the higher
bits (i.e. from bit-5 onwards a.k.a domain_nr >= 32) of the PCI domain
number gets truncated because of the shifted value casting to return
type of pci_domain_nr() which is 'int'. This for example is resulting
in same hwirq number for devices 0019:00:00.0 and 0039:00:00.0.

So, cast the PCI domain number to 'irq_hw_number_t' before left shifting
it to calculate hwirq number. Please note that this fixes the issue only
on 64-bit systems and doesn't change the behavior in 32-bit systems i.e.
the 32-bit systems continue to have the issue. Since the issue surfaces
only if there are too many PCIe controllers in the system which usually
is the case in modern server systems and they don't tend to run 32-bit
kernels.

Fixes: 3878eaefb89a ("PCI/MSI: Enhance core to support hierarchy irqdomain")
Tested-by: Shanker Donthineni <sdonthineni@nvidia.com>
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
V4:
* Added extra information in the change log about the impact of this patch
  in a 32-bit system as suggested by Thomas

V3:
* Addressed review comments from Thomas Gleixner
* Added Tested-By: Shanker Donthineni <sdonthineni@nvidia.com>

V2:
* Added Fixes tag

 drivers/pci/msi/irqdomain.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
index c8be056c248d..cfd84a899c82 100644
--- a/drivers/pci/msi/irqdomain.c
+++ b/drivers/pci/msi/irqdomain.c
@@ -61,7 +61,7 @@ static irq_hw_number_t pci_msi_domain_calc_hwirq(struct msi_desc *desc)
 
 	return (irq_hw_number_t)desc->msi_index |
 		pci_dev_id(dev) << 11 |
-		(pci_domain_nr(dev->bus) & 0xFFFFFFFF) << 27;
+		((irq_hw_number_t)(pci_domain_nr(dev->bus) & 0xFFFFFFFF)) << 27;
 }
 
 static void pci_msi_domain_set_desc(msi_alloc_info_t *arg,
-- 
2.25.1