ALSA: dice: restrict the driver to playback-only devices

At the moment, this driver supports only playback, while FFADO supports
(only) full-duplex devices.  So, prevent conflicts by not claiming
devices that would be better handled by FFADO.

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

2 files changed, 15 insertions, 4 deletions

diff --git a/sound/firewire/Kconfig b/sound/firewire/Kconfig
index 915330989412..b3e274fe4a77 100644
--- a/sound/firewire/Kconfig
+++ b/sound/firewire/Kconfig
@@ -12,14 +12,16 @@ config SND_FIREWIRE_LIB
         depends on SND_PCM
 
 config SND_DICE
-        tristate "DICE devices (EXPERIMENTAL)"
+        tristate "DICE-based DACs (EXPERIMENTAL)"
         select SND_HWDEP
         select SND_PCM
         select SND_FIREWIRE_LIB
         help
-          Say Y here to include support for many FireWire audio interfaces
-          based on the DICE chip family (DICE-II/Jr/Mini) from TC Applied
-          Technologies.
+          Say Y here to include support for many DACs based on the DICE
+          chip family (DICE-II/Jr/Mini) from TC Applied Technologies.
+
+          At the moment, this driver supports playback only.  If you
+          want to use devices that support capturing, use FFADO instead.
 
           To compile this driver as a module, choose M here: the module
           will be called snd-dice.
diff --git a/sound/firewire/dice.c b/sound/firewire/dice.c
index 49d630ba2d9f..6feee6614193 100644
--- a/sound/firewire/dice.c
+++ b/sound/firewire/dice.c
@@ -1128,6 +1128,7 @@ static int dice_interface_check(struct fw_unit *unit)
         int key, value, vendor = -1, model = -1, err;
         unsigned int category, i;
         __be32 pointers[ARRAY_SIZE(min_values)];
+        __be32 tx_data[4];
         __be32 version;
 
         /*
@@ -1171,6 +1172,14 @@ static int dice_interface_check(struct fw_unit *unit)
                         return -ENODEV;
         }
 
+        /* We support playback only. Let capture devices be handled by FFADO. */
+        err = snd_fw_transaction(unit, TCODE_READ_BLOCK_REQUEST,
+                                 DICE_PRIVATE_SPACE +
+                                 be32_to_cpu(pointers[2]) * 4,
+                                 tx_data, sizeof(tx_data), 0);
+        if (err < 0 || (tx_data[0] && tx_data[3]))
+                return -ENODEV;
+
         /*
          * Check that the implemented DICE driver specification major version
          * number matches.