This patch introduces a caif shared memory link layer driver
for ST-Ericsson's Thor M7400 LTE modem.

M7400 uses a ring-buffer in shared memory for transporting data from the modem.
Each ring-buffer element contains an array of caif frames. caif_xshm calls
napi_schedule() when receiving notification about incoming data.
The napi-poll function copies data from the ring-buffer to SKBs until
ring-buffer is empty, or quota is exceeded.

If transmit ring-buffer is full, it also uses napi for scheduling transmission
of queued transmit buffer.

Signed-off-by: Sjur Brændeland <redacted>
cc: netdev@vger.kernel.org
---
 drivers/net/caif/Kconfig     |   10 +
 drivers/net/caif/Makefile    |    1 +
 drivers/net/caif/caif_xshm.c |  935 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 946 insertions(+), 0 deletions(-)
 create mode 100644 drivers/net/caif/caif_xshm.c

diff --git a/drivers/net/caif/Kconfig b/drivers/net/caif/Kconfig
index abf4d7a..2861374 100644
--- a/drivers/net/caif/Kconfig
+++ b/drivers/net/caif/Kconfig

@@ -47,3 +47,13 @@ config CAIF_HSI
        The caif low level driver for CAIF over HSI.
        Be aware that if you enable this then you also need to
        enable a low-level HSI driver.
+
+config CAIF_XSHM
+	tristate "CAIF external memory protocol driver"
+	depends on XSHM && CAIF
+	default n
+	---help---
+	Say "yes" if you want to support CAIF over External Shared Memory (XSHM)