PCI: pci-bridge-emul: Fix emulation of W1C bits

The pci_bridge_emul_conf_write() function correctly clears W1C bits in
cfgspace cache, but it does not inform the underlying implementation
about the clear request: the .write_op() method is given the value with
these bits cleared.

This is wrong if the .write_op() needs to know which bits were requested
to be cleared.

Fix the value to be passed into the .write_op() method to have requested
W1C bits set, so that it can clear them.

Both pci-bridge-emul users (mvebu and aardvark) are compatible with this
change.

Link: https://lore.kernel.org/r/20211028185659.20329-2-kabel@kernel.org
Fixes: 23a5fba4 ("PCI: Introduce PCI bridge emulated config space common logic")
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org
Cc: Russell King <rmk+kernel@armlinux.org.uk>

drivers/pci/pci-bridge-emul.c

@@ -431,8 +431,21 @@ int pci_bridge_emul_conf_write(struct pci_bridge_emul *bridge, int where,
 	/* Clear the W1C bits */
 	new &= ~((value << shift) & (behavior[reg / 4].w1c & mask));
 
+	/* Save the new value with the cleared W1C bits into the cfgspace */
 	cfgspace[reg / 4] = cpu_to_le32(new);
 
+	/*
+	 * Clear the W1C bits not specified by the write mask, so that the
+	 * write_op() does not clear them.
+	 */
+	new &= ~(behavior[reg / 4].w1c & ~mask);
+
+	/*
+	 * Set the W1C bits specified by the write mask, so that write_op()
+	 * knows about that they are to be cleared.
+	 */
+	new |= (value << shift) & (behavior[reg / 4].w1c & mask);
+
 	if (write_op)
 		write_op(bridge, reg, old, new, mask);