stm class: Factor out default framing protocol

The STP framing pattern that the stm class implicitly applies to the
data payload is, in fact, a protocol. This patch moves the relevant code
out of the stm core into its own driver module.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 67 insertions, 0 deletions

diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
index 723e2d90083d..262e7891fb97 100644
--- a/drivers/hwtracing/stm/Kconfig
+++ b/drivers/hwtracing/stm/Kconfig
@@ -11,6 +11,21 @@ config STM
 
 if STM
 
+config STM_PROTO_BASIC
+        tristate "Basic STM framing protocol driver"
+        default CONFIG_STM
+        help
+          This is a simple framing protocol for sending data over STM
+          devices. This was the protocol that the STM framework used
+          exclusively until the MIPI SyS-T support was added. Use this
+          driver for compatibility with your existing STM setup.
+
+          The receiving side only needs to be able to decode the MIPI
+          STP protocol in order to extract the data.
+
+          If you want to be able to use the basic protocol or want the
+          backwards compatibility for your existing setup, say Y.
+
 config STM_DUMMY
         tristate "Dummy STM driver"
         help
diff --git a/drivers/hwtracing/stm/Makefile b/drivers/hwtracing/stm/Makefile
index effc19e5190f..1571de66eca4 100644
--- a/drivers/hwtracing/stm/Makefile
+++ b/drivers/hwtracing/stm/Makefile
@@ -3,6 +3,10 @@ obj-$(CONFIG_STM)	+= stm_core.o
 
 stm_core-y              := core.o policy.o
 
+obj-$(CONFIG_STM_PROTO_BASIC) += stm_p_basic.o
+
+stm_p_basic-y           := p_basic.o
+
 obj-$(CONFIG_STM_DUMMY) += dummy_stm.o
 
 obj-$(CONFIG_STM_SOURCE_CONSOLE)        += stm_console.o
diff --git a/drivers/hwtracing/stm/p_basic.c b/drivers/hwtracing/stm/p_basic.c
new file mode 100644
index 000000000000..8980a6a5fd6c
--- /dev/null
+++ b/drivers/hwtracing/stm/p_basic.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Basic framing protocol for STM devices.
+ * Copyright (c) 2018, Intel Corporation.
+ */
+
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/stm.h>
+#include "stm.h"
+
+static ssize_t basic_write(struct stm_data *data, struct stm_output *output,
+                           unsigned int chan, const char *buf, size_t count)
+{
+        unsigned int c = output->channel + chan;
+        unsigned int m = output->master;
+        const unsigned char nil = 0;
+        ssize_t sz;
+
+        sz = stm_data_write(data, m, c, true, buf, count);
+        if (sz > 0)
+                data->packet(data, m, c, STP_PACKET_FLAG, 0, 0, &nil);
+
+        return sz;
+}
+
+static const struct stm_protocol_driver basic_pdrv = {
+        .owner  = THIS_MODULE,
+        .name   = "p_basic",
+        .write  = basic_write,
+};
+
+static int basic_stm_init(void)
+{
+        return stm_register_protocol(&basic_pdrv);
+}
+
+static void basic_stm_exit(void)
+{
+        stm_unregister_protocol(&basic_pdrv);
+}
+
+module_init(basic_stm_init);
+module_exit(basic_stm_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("Basic STM framing protocol driver");
+MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@linux.intel.com>");