mailbox: pcc: Don't access an unmapped memory address space

The acpi_pcc_probe() may end up accessing memory outside of the PCCT
table space causing the kernel panic(). Increment the pcct_entry
pointer after parsing 'HW-reduced Communications Subspace' to fix
the problem. This change also enables the parsing of subtable at
index 0.

Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
Acked-by: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Shanker Donthineni

drivers/mailbox/pcc.c

@@ -367,15 +367,15 @@ static int __init acpi_pcc_probe(void)
 		struct acpi_generic_address *db_reg;
 		struct acpi_pcct_hw_reduced *pcct_ss;
 		pcc_mbox_channels[i].con_priv = pcct_entry;
-		pcct_entry = (struct acpi_subtable_header *)
-			((unsigned long) pcct_entry + pcct_entry->length);
 
 		/* If doorbell is in system memory cache the virt address */
 		pcct_ss = (struct acpi_pcct_hw_reduced *)pcct_entry;
 		db_reg = &pcct_ss->doorbell_register;
 		if (db_reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY)
 			pcc_doorbell_vaddr[i] = acpi_os_ioremap(db_reg->address,
 							db_reg->bit_width/8);
+		pcct_entry = (struct acpi_subtable_header *)
+			((unsigned long) pcct_entry + pcct_entry->length);
 	}
 
 	pcc_mbox_ctrl.num_chans = count;