[PATCH 1/2] firewire-core: add kernel API to construct multichannel isoc context

[Takashi Sakamoto]

In 1394 OHCI specification, IR context has several modes. One of mode
is 'multiChanMode'. For this mode, Linux FireWire stack has
FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL flag apart from FW_ISO_CONTEXT_RECEIVE,
and associated internal callback. However, code of firewire-core driver
includes cast of function callback for the mode and this brings
inconvenient to effort of Control Flow Integrity builds.

This commit is a preparation to remove the cast. A new kernel API for the
mode is added and existent API is specific for FW_ISO_CONTEXT_RECEIVE and
FW_ISO_CONTEXT_TRANSMIT modes. Actually, no in-kernel driver uses the mode
and the additional kernel API is never used at present.

Reported-by: Oscar Carter <oscar.carter at gmx.com>
Reference: https://lore.kernel.org/lkml/20200519173425.4724-1-oscar.carter@gmx.com/
Signed-off-by: Takashi Sakamoto <o-takashi at sakamocchi.jp>
---
 drivers/firewire/core-iso.c | 17 +++++++++++++++++
 include/linux/firewire.h    |  3 +++
 2 files changed, 20 insertions(+)

diff --git a/drivers/firewire/core-iso.c b/drivers/firewire/core-iso.c
index 185b0b78b3d6..07e967594f27 100644
--- a/drivers/firewire/core-iso.c
+++ b/drivers/firewire/core-iso.c
@@ -152,6 +152,23 @@ struct fw_iso_context *fw_iso_context_create(struct fw_card *card,
 }
 EXPORT_SYMBOL(fw_iso_context_create);
 
+struct fw_iso_context *fw_iso_mc_context_create(struct fw_card *card,
+		int type, int channel, int speed, size_t header_size,
+		fw_iso_mc_callback_t callback, void *callback_data)
+{
+	struct fw_iso_context *ctx;
+
+	ctx = fw_iso_context_create(card, type, channel, speed, header_size,
+				    NULL, callback_data);
+	if (IS_ERR(ctx))
+		return ctx;
+
+	ctx->callback.mc = callback;
+
+	return ctx;
+}
+EXPORT_SYMBOL(fw_iso_mc_context_create);
+
 void fw_iso_context_destroy(struct fw_iso_context *ctx)
 {
 	ctx->card->driver->free_iso_context(ctx);
diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index aec8f30ab200..9477814ab12a 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -453,6 +453,9 @@ struct fw_iso_context {
 struct fw_iso_context *fw_iso_context_create(struct fw_card *card,
 		int type, int channel, int speed, size_t header_size,
 		fw_iso_callback_t callback, void *callback_data);
+struct fw_iso_context *fw_iso_mc_context_create(struct fw_card *card,
+		int type, int channel, int speed, size_t header_size,
+		fw_iso_mc_callback_t callback, void *callback_data);
 int fw_iso_context_set_channels(struct fw_iso_context *ctx, u64 *channels);
 int fw_iso_context_queue(struct fw_iso_context *ctx,
 			 struct fw_iso_packet *packet,
-- 
2.25.1