linux-kernel - [PATCH 5.16 0574/1017] PCI: Reduce warnings on possible RW1C corruption

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Message-Id: <20220405070411.318299247@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:24:47 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>,
        Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Rob Herring <robh@...nel.org>,
        Scott Branden <scott.branden@...adcom.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.16 0574/1017] PCI: Reduce warnings on possible RW1C corruption

From: Mark Tomlinson <mark.tomlinson@...iedtelesis.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@...nel.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@...iedtelesis.co.nz>
Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
Reviewed-by: Rob Herring <robh@...nel.org>
Acked-by: Scott Branden <scott.branden@...adcom.com>
Signed-off-by: Sasha Levin <sashal@...nel.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 46935695cfb9..8d0d1f61c650 100644
--- 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 18a75c8e615c..2d6118937d07 100644
--- 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)
-- 
2.34.1