PCI: Reduce warnings on possible RW1C corruption

[ Upstream commit 92c45b63ce22c8898aa41806e8d6692bcd577510 ]

For hardware that only supports 32-bit writes to PCI there is the
possibility of clearing RW1C (write-one-to-clear) bits. A rate-limited
messages was introduced by fb2659230120, but rate-limiting is not the best
choice here. Some devices may not show the warnings they should if another
device has just produced a bunch of warnings. Also, the number of messages
can be a nuisance on devices which are otherwise working fine.

Change the ratelimit to a single warning per bus. This ensures no bus is
'starved' of emitting a warning and also that there isn't a continuous
stream of warnings. It would be preferable to have a warning per device,
but the pci_dev structure is not available here, and a lookup from devfn
would be far too slow.

Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Fixes: fb2659230120 ("PCI: Warn on possible RW1C corruption for sub-32 bit config writes")
Link: https://lore.kernel.org/r/20200806041455.11070-1-mark.tomlinson@alliedtelesis.co.nz
Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 4693569..8d0d1f6 100644 (file)
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -160,9 +160,12 @@ int pci_generic_config_write32(struct pci_bus *bus, unsigned int devfn,
         * write happen to have any RW1C (write-one-to-clear) bits set, we
         * just inadvertently cleared something we shouldn't have.
         */
-       dev_warn_ratelimited(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
-                            size, pci_domain_nr(bus), bus->number,
-                            PCI_SLOT(devfn), PCI_FUNC(devfn), where);
+       if (!bus->unsafe_warn) {
+               dev_warn(&bus->dev, "%d-byte config write to %04x:%02x:%02x.%d offset %#x may corrupt adjacent RW1C bits\n",
+                        size, pci_domain_nr(bus), bus->number,
+                        PCI_SLOT(devfn), PCI_FUNC(devfn), where);
+               bus->unsafe_warn = 1;
+       }
 
        mask = ~(((1 << (size * 8)) - 1) << ((where & 0x3) * 8));
        tmp = readl(addr) & mask;

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 152a4d7..9d6e752 100644 (file)
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -656,6 +656,7 @@ struct pci_bus {
        struct bin_attribute    *legacy_io;     /* Legacy I/O for this bus */
        struct bin_attribute    *legacy_mem;    /* Legacy mem */
        unsigned int            is_added:1;
+       unsigned int            unsafe_warn:1;  /* warned about RW1C config write */
 };
 
 #define to_pci_bus(n)  container_of(n, struct pci_bus, dev)