[RFC/RFT] ssb: Avoid system hang when SPROM read fails

[Larry Finger]

In kernel Bugzilla #15825, the OP reports a case of intermittent reading
of the SPROM. If such reads fail, the box hangs. Thanks to careful testing
by bugzillakernelorg at lez.ath.cx has shown that the first read of the
SPROM returns 0xFFFF with the hang happening on the next read.

The source of the read failure is still under investigation; however,
this patch does avoid the system hang.

Signed-off-by: Larry Finger <Larry.Finger at lwfinger.net>
---

John,

Does this patch avoid the system hang on your box?

Larry
---

===================================================================
--- wireless-testing.orig/drivers/ssb/pci.c
+++ wireless-testing/drivers/ssb/pci.c
@@ -253,6 +253,11 @@ static int sprom_do_read(struct ssb_bus
 {
 	int i;
 
+	/* Check if SPROM can be read */
+	if (ioread16(bus->mmio + SSB_SPROM_BASE) == 0xFFFF) {
+		ssb_printk(KERN_ERR PFX "Unable to read SPROM\n");
+		return -ENODEV;
+	}
 	for (i = 0; i < bus->sprom_size; i++)
 		sprom[i] = ioread16(bus->mmio + SSB_SPROM_BASE + (i * 2));
 
@@ -625,17 +630,23 @@ static int ssb_pci_sprom_get(struct ssb_
 	if (!buf)
 		goto out;
 	bus->sprom_size = SSB_SPROMSIZE_WORDS_R123;
-	sprom_do_read(bus, buf);
+	err = sprom_do_read(bus, buf);
+	if (err)
+		goto out_free;
 	err = sprom_check_crc(buf, bus->sprom_size);
 	if (err) {
 		/* try for a 440 byte SPROM - revision 4 and higher */
 		kfree(buf);
 		buf = kcalloc(SSB_SPROMSIZE_WORDS_R4, sizeof(u16),
 			      GFP_KERNEL);
-		if (!buf)
+		if (!buf) {
+			err = -ENOMEM;
 			goto out;
+		}
 		bus->sprom_size = SSB_SPROMSIZE_WORDS_R4;
-		sprom_do_read(bus, buf);
+		err = sprom_do_read(bus, buf);
+		if (err)
+			goto out_free;
 		err = sprom_check_crc(buf, bus->sprom_size);
 		if (err) {
 			/* All CRC attempts failed.