PCI/ASPM: Make sysfs link_state_store() consistent with link_state_show()

If CONFIG_PCIEASPM_DEBUG is set, then PCI devices have a link_state
attribute.  Reading that attribute shows the state as a bit mask: 1
means L0S upstream, 2 means L0S downstream, and 4 means L1.

Oddly, writing to link_state is inconsistent and gets translated, leading
to mysterious results in which the value you store isn't comparable the
value you load back out.

Fix it by making link_state_store() match link_state_show().

[bhelgaas: Check "aspm_disabled" *before* validating input.  When
"aspm_disabled" is set, this changes the error for invalid input from
-EINVAL to -EPERM.]
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pcie/aspm.c

@@ -834,21 +834,15 @@ static ssize_t link_state_store(struct device *dev,
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct pcie_link_state *link, *root = pdev->link_state->root;
-	u32 val, state = 0;
-
-	if (kstrtouint(buf, 10, &val))
-		return -EINVAL;
+	u32 state;
 
 	if (aspm_disabled)
 		return -EPERM;
-	if (n < 1 || val > 3)
-		return -EINVAL;
 
-	/* Convert requested state to ASPM state */
-	if (val & PCIE_LINK_STATE_L0S)
-		state |= ASPM_STATE_L0S;
-	if (val & PCIE_LINK_STATE_L1)
-		state |= ASPM_STATE_L1;
+	if (kstrtouint(buf, 10, &state))
+		return -EINVAL;
+	if ((state & ~ASPM_STATE_ALL) != 0)
+		return -EINVAL;
 
 	down_read(&pci_bus_sem);
 	mutex_lock(&aspm_lock);