PCI: Warn on possible RW1C corruption for sub-32 bit config writes

Hardware that supports only 32-bit config writes is not spec-compliant.
For example, if software performs a 16-bit write, we must do a 32-bit read,
merge in the 16 bits we intend to write, followed by a 32-bit write.  If
the 16 bits we *don't* intend to write happen to have any RW1C (write-one-
to-clear) bits set, we just inadvertently cleared something we shouldn't
have.

Add a rate-limited warning when we do sub-32 bit config writes.  Remove
similar probe-time warnings from some of the affected host bridge drivers.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Enthusiastically-Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Shawn Lin <shawn.lin@rock-chips.com>	# rockchip
Acked-by: Thierry Reding <treding@nvidia.com>

drivers/pci/access.c

@@ -142,10 +142,22 @@ int pci_generic_config_write32(struct pci_bus *bus, unsigned int devfn,
 	if (size == 4) {
 		writel(val, addr);
 		return PCIBIOS_SUCCESSFUL;
-	} else {
-		mask = ~(((1 << (size * 8)) - 1) << ((where & 0x3) * 8));
 	}
 
+	/*
+	 * In general, hardware that supports only 32-bit writes on PCI is
+	 * not spec-compliant.  For example, software may perform a 16-bit
+	 * write.  If the hardware only supports 32-bit accesses, we must
+	 * do a 32-bit read, merge in the 16 bits we intend to write,
+	 * followed by a 32-bit write.  If the 16 bits we *don't* intend to
+	 * 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);
+
+	mask = ~(((1 << (size * 8)) - 1) << ((where & 0x3) * 8));
 	tmp = readl(addr) & mask;
 	tmp |= val << ((where & 0x3) * 8);
 	writel(tmp, addr);

drivers/pci/host/pcie-hisi.c

@@ -194,8 +194,6 @@ static int hisi_pcie_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	dev_warn(dev, "only 32-bit config accesses supported; smaller writes may corrupt adjacent RW1C fields\n");
-
 	return 0;
 }
 

drivers/pci/host/pcie-rockchip.c

@@ -1187,9 +1187,6 @@ static int rockchip_pcie_probe(struct platform_device *pdev)
 		pcie_bus_configure_settings(child);
 
 	pci_bus_add_devices(bus);
-
-	dev_warn(dev, "only 32-bit config accesses supported; smaller writes may corrupt adjacent RW1C fields\n");
-
 	return err;
 
 err_vpcie: