firewire: core: add CSR MAINT_UTILITY support

Implement the MAIN_UTILITY register, which is utterly optional
but useful as a safe target for diagnostic read/write/broadcast
transactions.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

2 files changed, 12 insertions, 0 deletions

diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index a61eb3fb9573..dd8ef650a7cb 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -1140,6 +1140,15 @@ static void handle_registers(struct fw_card *card, struct fw_request *request,
                         rcode = RCODE_TYPE_ERROR;
                 break;
 
+        case CSR_MAINT_UTILITY:
+                if (tcode == TCODE_READ_QUADLET_REQUEST)
+                        *data = card->maint_utility_register;
+                else if (tcode == TCODE_WRITE_QUADLET_REQUEST)
+                        card->maint_utility_register = *data;
+                else
+                        rcode = RCODE_TYPE_ERROR;
+                break;
+
         case CSR_BROADCAST_CHANNEL:
                 if (tcode == TCODE_READ_QUADLET_REQUEST)
                         *data = cpu_to_be32(card->broadcast_channel);
diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index a50377d91254..f1160e831dad 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -38,6 +38,7 @@
 #define CSR_CHANNELS_AVAILABLE          0x224
 #define CSR_CHANNELS_AVAILABLE_HI       0x224
 #define CSR_CHANNELS_AVAILABLE_LO       0x228
+#define CSR_MAINT_UTILITY               0x230
 #define CSR_BROADCAST_CHANNEL           0x234
 #define CSR_CONFIG_ROM                  0x400
 #define CSR_CONFIG_ROM_END              0x800
@@ -122,6 +123,8 @@ struct fw_card {
         bool broadcast_channel_allocated;
         u32 broadcast_channel;
         __be32 topology_map[(CSR_TOPOLOGY_MAP_END - CSR_TOPOLOGY_MAP) / 4];
+
+        __be32 maint_utility_register;
 };
 
 struct fw_attribute_group {