firewire: core: detect device quirk when reading configuration ROM

Every time the bus manager runs, the cached configuration ROM content of
the IRM device is investigated to detect device-specific quirks. This
detection can be performed in advance when reading the configuration ROM.

This commit adds device quirk flags to the fw_device structure, and
initializes them after reading the bus information block of the
configuration ROM. The quirk flags are immutable once the configuration
ROM has been read. Although they are likely accessed concurrently only by
the bus manager, this commit ensures safe access by preventing torn writes
and reads using the WRITE_ONCE()/READ_ONCE() macros.

Link: https://lore.kernel.org/r/20251013140311.97159-2-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index 6d208769d456..161829cfcc00 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -170,6 +170,14 @@ struct fw_attribute_group {
 	struct attribute *attrs[13];
 };
 
+enum fw_device_quirk {
+	// See afa1282a35d3 ("firewire: core: check for 1394a compliant IRM, fix inaccessibility of Sony camcorder").
+	FW_DEVICE_QUIRK_IRM_IS_1394_1995_ONLY = BIT(0),
+
+	// See a509e43ff338 ("firewire: core: fix unstable I/O with Canon camcorder").
+	FW_DEVICE_QUIRK_IRM_IGNORES_BUS_MANAGER = BIT(1),
+};
+
 enum fw_device_state {
 	FW_DEVICE_INITIALIZING,
 	FW_DEVICE_RUNNING,
@@ -203,6 +211,9 @@ struct fw_device {
 	struct fw_card *card;
 	struct device device;
 
+	// A set of enum fw_device_quirk.
+	int quirks;
+
 	struct mutex client_list_mutex;
 	struct list_head client_list;