[PATCH 5.17 0635/1126] PCI: Reduce warnings on possible RW1C corruption

Greg Kroah-Hartman
2022-04-05T08:24:11Z

From: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>

[ 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>
---
drivers/pci/access.c | 9 ++++++---
include/linux/pci.h | 1 +
2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 0d9f6b21babb..708c7529647f 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -159,9 +159,12 @@ 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 8253a5413d7c..678fecdf6b81 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -668,6 +668,7 @@ 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)
--
2.34.1