[PATCH v3 03/14] greybus: cpc: use socket buffers instead of gb_message in TX path

["Damien Riégel" <damien.riegel@silabs.com>]

CPC comes with its own header, whose support is added in a future commit
of this series. Without skb, the CPC host device drivers have to get two
pointers to get a full packet: one pointer to the CPC header and one
pointer to the GB message.

In order to make implementations simpler, convert the GB message into an
SKB in the `message_send()` operation. That way, CPC internally works
only with SKBs, and only convert back to GB messages when notifying
Greybus core that a message has been transmitted or received.

Signed-off-by: Damien Riégel <damien.riegel@silabs.com>
---
 drivers/greybus/cpc/cpc.h   | 11 +++++++++-
 drivers/greybus/cpc/cport.c | 11 ++++++++--
 drivers/greybus/cpc/host.c  | 41 ++++++++++++++++++++++++++++++++++---
 drivers/greybus/cpc/host.h  |  7 ++++---
 4 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/drivers/greybus/cpc/cpc.h b/drivers/greybus/cpc/cpc.h
index 3915a7fbc4f..d9f8f60913a 100644
--- a/drivers/greybus/cpc/cpc.h
+++ b/drivers/greybus/cpc/cpc.h
@@ -24,6 +24,15 @@ struct cpc_cport {
 struct cpc_cport *cpc_cport_alloc(u16 cport_id, gfp_t gfp_mask);
 void cpc_cport_release(struct cpc_cport *cport);
 
-int cpc_cport_message_send(struct cpc_cport *cport, struct gb_message *message, gfp_t gfp_mask);
+int cpc_cport_transmit(struct cpc_cport *cport, struct sk_buff *skb);
+
+struct cpc_skb_cb {
+	struct cpc_cport *cport;
+
+	/* Keep track of the GB message the skb originates from */
+	struct gb_message *gb_message;
+};
+
+#define CPC_SKB_CB(__skb) ((struct cpc_skb_cb *)&((__skb)->cb[0]))
 
 #endif
diff --git a/drivers/greybus/cpc/cport.c b/drivers/greybus/cpc/cport.c
index 88bdb2f8182..ed0b8e8b0d7 100644
--- a/drivers/greybus/cpc/cport.c
+++ b/drivers/greybus/cpc/cport.c
@@ -31,7 +31,14 @@ void cpc_cport_release(struct cpc_cport *cport)
 	kfree(cport);
 }
 
-int cpc_cport_message_send(struct cpc_cport *cport, struct gb_message *message, gfp_t gfp_mask)
+/**
+ * cpc_cport_transmit() - Transmit skb over cport.
+ * @cport: cport.
+ * @skb: skb to be transmitted.
+ */
+int cpc_cport_transmit(struct cpc_cport *cport, struct sk_buff *skb)
 {
-	return cport->cpc_hd->driver->message_send(cport->cpc_hd, cport->id, message, gfp_mask);
+	struct cpc_host_device *cpc_hd = cport->cpc_hd;
+
+	return cpc_hd_send_skb(cpc_hd, skb);
 }
diff --git a/drivers/greybus/cpc/host.c b/drivers/greybus/cpc/host.c
index 3dda5b06590..a3acfc9bfca 100644
--- a/drivers/greybus/cpc/host.c
+++ b/drivers/greybus/cpc/host.c
@@ -6,6 +6,7 @@
 #include <linux/err.h>
 #include <linux/greybus.h>
 #include <linux/module.h>
+#include <linux/skbuff.h>
 
 #include "cpc.h"
 #include "host.h"
@@ -38,6 +39,8 @@ static int cpc_hd_message_send(struct cpc_host_device *cpc_hd, u16 cport_id,
 			       struct gb_message *message, gfp_t gfp_mask)
 {
 	struct cpc_cport *cport;
+	struct sk_buff *skb;
+	unsigned int size;
 
 	cport = cpc_hd_get_cport(cpc_hd, cport_id);
 	if (!cport) {
@@ -45,7 +48,18 @@ static int cpc_hd_message_send(struct cpc_host_device *cpc_hd, u16 cport_id,
 		return -EINVAL;
 	}
 
-	return cpc_cport_message_send(cport, message, gfp_mask);
+	size = sizeof(*message->header) + message->payload_size;
+	skb = alloc_skb(size, gfp_mask);
+	if (!skb)
+		return -ENOMEM;
+
+	/* Header and payload are already contiguous in Greybus message */
+	skb_put_data(skb, message->buffer, sizeof(*message->header) + message->payload_size);
+
+	CPC_SKB_CB(skb)->cport = cport;
+	CPC_SKB_CB(skb)->gb_message = message;
+
+	return cpc_cport_transmit(cport, skb);
 }
 
 static int cpc_hd_cport_allocate(struct cpc_host_device *cpc_hd, int cport_id, unsigned long flags)
@@ -149,8 +163,8 @@ struct cpc_host_device *cpc_hd_create(struct cpc_hd_driver *driver, struct devic
 	struct cpc_host_device *cpc_hd;
 	struct gb_host_device *hd;
 
-	if ((!driver->message_send) || (!driver->message_cancel)) {
-		dev_err(parent, "missing mandatory callbacks\n");
+	if (!driver->transmit) {
+		dev_err(parent, "missing mandatory callback\n");
 		return ERR_PTR(-EINVAL);
 	}
 
@@ -186,12 +200,33 @@ void cpc_hd_del(struct cpc_host_device *cpc_hd)
 }
 EXPORT_SYMBOL_GPL(cpc_hd_del);
 
+void cpc_hd_message_sent(struct sk_buff *skb, int status)
+{
+	struct cpc_host_device *cpc_hd = CPC_SKB_CB(skb)->cport->cpc_hd;
+	struct gb_host_device *hd = cpc_hd->gb_hd;
+
+	greybus_message_sent(hd, CPC_SKB_CB(skb)->gb_message, status);
+}
+EXPORT_SYMBOL_GPL(cpc_hd_message_sent);
+
 void cpc_hd_rcvd(struct cpc_host_device *cpc_hd, u16 cport_id, u8 *data, size_t length)
 {
 	greybus_data_rcvd(cpc_hd->gb_hd, cport_id, data, length);
 }
 EXPORT_SYMBOL_GPL(cpc_hd_rcvd);
 
+/**
+ * cpc_hd_send_skb() - Queue a socket buffer for transmission.
+ * @cpc_hd: Host device to send SKB over.
+ * @skb: SKB to send.
+ */
+int cpc_hd_send_skb(struct cpc_host_device *cpc_hd, struct sk_buff *skb)
+{
+	const struct cpc_hd_driver *drv = cpc_hd->driver;
+
+	return drv->transmit(cpc_hd, skb);
+}
+
 MODULE_DESCRIPTION("Greybus over CPC");
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Silicon Laboratories, Inc.");
diff --git a/drivers/greybus/cpc/host.h b/drivers/greybus/cpc/host.h
index c3f2f56a939..191b5e394a6 100644
--- a/drivers/greybus/cpc/host.h
+++ b/drivers/greybus/cpc/host.h
@@ -18,9 +18,7 @@ struct cpc_cport;
 struct cpc_host_device;
 
 struct cpc_hd_driver {
-	int (*message_send)(struct cpc_host_device *hd, u16 dest_cport_id,
-			    struct gb_message *message, gfp_t gfp_mask);
-	void (*message_cancel)(struct gb_message *message);
+	int (*transmit)(struct cpc_host_device *hd, struct sk_buff *skb);
 };
 
 /**
@@ -48,5 +46,8 @@ int cpc_hd_add(struct cpc_host_device *cpc_hd);
 void cpc_hd_put(struct cpc_host_device *cpc_hd);
 void cpc_hd_del(struct cpc_host_device *cpc_hd);
 void cpc_hd_rcvd(struct cpc_host_device *cpc_hd, u16 cport_id, u8 *data, size_t length);
+void cpc_hd_message_sent(struct sk_buff *skb, int status);
+
+int cpc_hd_send_skb(struct cpc_host_device *cpc_hd, struct sk_buff *skb);
 
 #endif
-- 
2.52.0