[PATCH v4] firmware: imx: Add DSP IPC protocol interface

[PATCH v4] firmware: imx: Add DSP IPC protocol interface

[Daniel Baluta]

Some of i.MX8 processors (e.g i.MX8QM, i.MX8QXP) contain
the Tensilica HiFi4 DSP for advanced pre- and post-audio
processing.

The communication between Host CPU and DSP firmware is
taking place using a shared memory area for message passing
and a dedicated Messaging Unit for notifications.

DSP IPC protocol offers a doorbell interface using
imx-mailbox API.

We use 4 MU channels (2 x TXDB, 2 x RXDB) to implement a
request-reply protocol.

Connection 0 (txdb0, rxdb0):
        - Host writes messasge to shared memory [SHMEM]
	- Host sends a request [MU]
	- DSP handles request [SHMEM]
	- DSP sends reply [MU]

Connection 1 (txdb1, rxdb1):
	- DSP writes a message to shared memory [SHMEM]
	- DSP sends a request [MU]
	- Host handles request [SHMEM]
	- Host sends reply [MU]

The protocol interface will be used by a Host client to
communicate with the DSP. First client will be the i.MX8
part from Sound Open Firmware infrastructure.

The protocol offers the following interface:

On Tx:
   - imx_dsp_ring_doorbell, will be called to notify the DSP
   that it needs to handle a request.

On Rx:
   - clients need to provide two callbacks:
	.handle_reply
	.handle_request
  - the callbacks will be used by the protocol on
    notification arrival from DSP.

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
---
Changes since v3:
	- Added remove function

 drivers/firmware/imx/Kconfig     |  11 +++
 drivers/firmware/imx/Makefile    |   1 +
 drivers/firmware/imx/imx-dsp.c   | 155 +++++++++++++++++++++++++++++++
 include/linux/firmware/imx/dsp.h |  67 +++++++++++++
 4 files changed, 234 insertions(+)
 create mode 100644 drivers/firmware/imx/imx-dsp.c
 create mode 100644 include/linux/firmware/imx/dsp.h

diff --git a/drivers/firmware/imx/Kconfig b/drivers/firmware/imx/Kconfig
index 42b566f8903f..0dbee32da4c6 100644
--- a/drivers/firmware/imx/Kconfig
+++ b/drivers/firmware/imx/Kconfig
@@ -1,4 +1,15 @@
 # SPDX-License-Identifier: GPL-2.0-only
+config IMX_DSP
+	bool "IMX DSP Protocol driver"
+	depends on IMX_MBOX
+	help
+	  This enables DSP IPC protocol between host AP (Linux)
+	  and the firmware running on DSP.
+	  DSP exists on some i.MX8 processors (e.g i.MX8QM, i.MX8QXP).
+
+	  It acts like a doorbell. Client might use shared memory to
+	  exchange information with DSP side.
+
 config IMX_SCU
 	bool "IMX SCU Protocol driver"
 	depends on IMX_MBOX
diff --git a/drivers/firmware/imx/Makefile b/drivers/firmware/imx/Makefile
index 802c4ad8e8f9..08bc9ddfbdfb 100644
--- a/drivers/firmware/imx/Makefile
+++ b/drivers/firmware/imx/Makefile
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_IMX_DSP)		+= imx-dsp.o
 obj-$(CONFIG_IMX_SCU)		+= imx-scu.o misc.o imx-scu-irq.o
 obj-$(CONFIG_IMX_SCU_PD)	+= scu-pd.o
diff --git a/drivers/firmware/imx/imx-dsp.c b/drivers/firmware/imx/imx-dsp.c
new file mode 100644
index 000000000000..a43d2db5cbdb
--- /dev/null
+++ b/drivers/firmware/imx/imx-dsp.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2019 NXP
+ *  Author: Daniel Baluta <daniel.baluta@nxp.com>
+ *
+ * Implementation of the DSP IPC interface (host side)
+ */
+
+#include <linux/firmware/imx/dsp.h>
+#include <linux/kernel.h>
+#include <linux/mailbox_client.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+/*
+ * imx_dsp_ring_doorbell - triggers an interrupt on the other side (DSP)
+ *
+ * @dsp: DSP IPC handle
+ * @chan_idx: index of the channel where to trigger the interrupt
+ *
+ * Returns non-negative value for success, negative value for error
+ */
+int imx_dsp_ring_doorbell(struct imx_dsp_ipc *ipc, unsigned int idx)
+{
+	int ret;
+	struct imx_dsp_chan *dsp_chan;
+
+	if (idx >= DSP_MU_CHAN_NUM)
+		return -EINVAL;
+
+	dsp_chan = &ipc->chans[idx];
+	ret = mbox_send_message(dsp_chan->ch, NULL);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(imx_dsp_ring_doorbell);
+
+/*
+ * imx_dsp_handle_rx - rx callback used by imx mailbox
+ *
+ * @c: mbox client
+ * @msg: message received
+ *
+ * Users of DSP IPC will need to privde handle_reply and handle_request
+ * callbacks.
+ */
+static void imx_dsp_handle_rx(struct mbox_client *c, void *msg)
+{
+	struct imx_dsp_chan *chan = container_of(c, struct imx_dsp_chan, cl);
+
+	if (chan->idx == 0) {
+		chan->ipc->ops->handle_reply(chan->ipc);
+	} else {
+		chan->ipc->ops->handle_request(chan->ipc);
+		imx_dsp_ring_doorbell(chan->ipc, 1);
+	}
+}
+
+static int imx_dsp_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct imx_dsp_ipc *dsp_ipc;
+	struct imx_dsp_chan *dsp_chan;
+	struct mbox_client *cl;
+	char *chan_name;
+	int ret;
+	int i, j;
+
+	device_set_of_node_from_dev(&pdev->dev, pdev->dev.parent);
+
+	dsp_ipc = devm_kzalloc(dev, sizeof(*dsp_ipc), GFP_KERNEL);
+	if (!dsp_ipc)
+		return -ENOMEM;
+
+	for (i = 0; i < DSP_MU_CHAN_NUM; i++) {
+		if (i < 2)
+			chan_name = kasprintf(GFP_KERNEL, "txdb%d", i);
+		else
+			chan_name = kasprintf(GFP_KERNEL, "rxdb%d", i - 2);
+
+		if (!chan_name)
+			return -ENOMEM;
+
+		dsp_chan = &dsp_ipc->chans[i];
+		cl = &dsp_chan->cl;
+		cl->dev = dev;
+		cl->tx_block = false;
+		cl->knows_txdone = true;
+		cl->rx_callback = imx_dsp_handle_rx;
+
+		dsp_chan->ipc = dsp_ipc;
+		dsp_chan->idx = i % 2;
+		dsp_chan->ch = mbox_request_channel_byname(cl, chan_name);
+		if (IS_ERR(dsp_chan->ch)) {
+			ret = PTR_ERR(dsp_chan->ch);
+			if (ret != -EPROBE_DEFER)
+				dev_err(dev, "Failed to request mbox chan %s ret %d\n",
+					chan_name, ret);
+			goto out;
+		}
+
+		dev_dbg(dev, "request mbox chan %s\n", chan_name);
+		/* chan_name is not used anymore by framework */
+		kfree(chan_name);
+	}
+
+	dsp_ipc->dev = dev;
+
+	dev_set_drvdata(dev, dsp_ipc);
+
+	dev_info(dev, "NXP i.MX DSP IPC initialized\n");
+
+	return devm_of_platform_populate(dev);
+out:
+	kfree(chan_name);
+	for (j = 0; j < i; j++) {
+		dsp_chan = &dsp_ipc->chans[j];
+		mbox_free_channel(dsp_chan->ch);
+	}
+
+	return ret;
+}
+
+static int imx_dsp_remove(struct platform_device *pdev)
+{
+	struct imx_dsp_chan *dsp_chan;
+	struct imx_dsp_ipc *dsp_ipc;
+	int i;
+
+	dsp_ipc = dev_get_drvdata(&pdev->dev);
+
+	for (i = 0; i < DSP_MU_CHAN_NUM; i++) {
+		dsp_chan = &dsp_ipc->chans[i];
+		mbox_free_channel(dsp_chan->ch);
+	}
+
+	return 0;
+}
+
+static struct platform_driver imx_dsp_driver = {
+	.driver = {
+		.name = "imx-dsp",
+	},
+	.probe = imx_dsp_probe,
+	.remove = imx_dsp_remove,
+};
+builtin_platform_driver(imx_dsp_driver);
+
+MODULE_AUTHOR("Daniel Baluta <daniel.baluta@nxp.com>");
+MODULE_DESCRIPTION("IMX DSP IPC protocol driver");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/firmware/imx/dsp.h b/include/linux/firmware/imx/dsp.h
new file mode 100644
index 000000000000..7562099c9e46
--- /dev/null
+++ b/include/linux/firmware/imx/dsp.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2019 NXP
+ *
+ * Header file for the DSP IPC implementation
+ */
+
+#ifndef _IMX_DSP_IPC_H
+#define _IMX_DSP_IPC_H
+
+#include <linux/device.h>
+#include <linux/types.h>
+#include <linux/mailbox_client.h>
+
+#define DSP_MU_CHAN_NUM		4
+
+struct imx_dsp_chan {
+	struct imx_dsp_ipc *ipc;
+	struct mbox_client cl;
+	struct mbox_chan *ch;
+	char *name;
+	int idx;
+};
+
+struct imx_dsp_ops {
+	void (*handle_reply)(struct imx_dsp_ipc *ipc);
+	void (*handle_request)(struct imx_dsp_ipc *ipc);
+};
+
+struct imx_dsp_ipc {
+	/* Host <-> DSP communication uses 2 txdb and 2 rxdb channels */
+	struct imx_dsp_chan chans[DSP_MU_CHAN_NUM];
+	struct device *dev;
+	struct imx_dsp_ops *ops;
+	void *private_data;
+};
+
+static inline void imx_dsp_set_data(struct imx_dsp_ipc *ipc, void *data)
+{
+	if (!ipc)
+		return;
+
+	ipc->private_data = data;
+}
+
+static inline void *imx_dsp_get_data(struct imx_dsp_ipc *ipc)
+{
+	if (!ipc)
+		return NULL;
+
+	return ipc->private_data;
+}
+
+#if IS_ENABLED(CONFIG_IMX_DSP)
+
+int imx_dsp_ring_doorbell(struct imx_dsp_ipc *dsp, unsigned int chan_idx);
+
+#else
+
+static inline int imx_dsp_ring_doorbell(struct imx_dsp_ipc *ipc,
+					unsigned int chan_idx)
+{
+	return -ENOTSUPP;
+}
+
+#endif
+#endif /* _IMX_DSP_IPC_H */
-- 
2.17.1

Re: [PATCH v4] firmware: imx: Add DSP IPC protocol interface

[Daniel Baluta]

Hi Shawn,

Can you please have a look at this when you have some time?

Basically, we need this patch for imx8 SOF Linux driver:

https://github.com/thesofproject/linux/pull/1048

I already got:

Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>

For an older version of this patch.

thanks,
Daniel.

On Thu, Aug 1, 2019 at 1:02 PM Daniel Baluta <daniel.baluta@nxp.com> wrote:
>
> Some of i.MX8 processors (e.g i.MX8QM, i.MX8QXP) contain
> the Tensilica HiFi4 DSP for advanced pre- and post-audio
> processing.
>
> The communication between Host CPU and DSP firmware is
> taking place using a shared memory area for message passing
> and a dedicated Messaging Unit for notifications.
>
> DSP IPC protocol offers a doorbell interface using
> imx-mailbox API.
>
> We use 4 MU channels (2 x TXDB, 2 x RXDB) to implement a
> request-reply protocol.
>
> Connection 0 (txdb0, rxdb0):
>         - Host writes messasge to shared memory [SHMEM]
>         - Host sends a request [MU]
>         - DSP handles request [SHMEM]
>         - DSP sends reply [MU]
>
> Connection 1 (txdb1, rxdb1):
>         - DSP writes a message to shared memory [SHMEM]
>         - DSP sends a request [MU]
>         - Host handles request [SHMEM]
>         - Host sends reply [MU]
>
> The protocol interface will be used by a Host client to
> communicate with the DSP. First client will be the i.MX8
> part from Sound Open Firmware infrastructure.
>
> The protocol offers the following interface:
>
> On Tx:
>    - imx_dsp_ring_doorbell, will be called to notify the DSP
>    that it needs to handle a request.
>
> On Rx:
>    - clients need to provide two callbacks:
>         .handle_reply
>         .handle_request
>   - the callbacks will be used by the protocol on
>     notification arrival from DSP.
>
> Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
> ---
> Changes since v3:
>         - Added remove function
>
>  drivers/firmware/imx/Kconfig     |  11 +++
>  drivers/firmware/imx/Makefile    |   1 +
>  drivers/firmware/imx/imx-dsp.c   | 155 +++++++++++++++++++++++++++++++
>  include/linux/firmware/imx/dsp.h |  67 +++++++++++++
>  4 files changed, 234 insertions(+)
>  create mode 100644 drivers/firmware/imx/imx-dsp.c
>  create mode 100644 include/linux/firmware/imx/dsp.h
>
> diff --git a/drivers/firmware/imx/Kconfig b/drivers/firmware/imx/Kconfig
> index 42b566f8903f..0dbee32da4c6 100644
> --- a/drivers/firmware/imx/Kconfig
> +++ b/drivers/firmware/imx/Kconfig
> @@ -1,4 +1,15 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> +config IMX_DSP
> +       bool "IMX DSP Protocol driver"
> +       depends on IMX_MBOX
> +       help
> +         This enables DSP IPC protocol between host AP (Linux)
> +         and the firmware running on DSP.
> +         DSP exists on some i.MX8 processors (e.g i.MX8QM, i.MX8QXP).
> +
> +         It acts like a doorbell. Client might use shared memory to
> +         exchange information with DSP side.
> +
>  config IMX_SCU
>         bool "IMX SCU Protocol driver"
>         depends on IMX_MBOX
> diff --git a/drivers/firmware/imx/Makefile b/drivers/firmware/imx/Makefile
> index 802c4ad8e8f9..08bc9ddfbdfb 100644
> --- a/drivers/firmware/imx/Makefile
> +++ b/drivers/firmware/imx/Makefile
> @@ -1,3 +1,4 @@
>  # SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_IMX_DSP)          += imx-dsp.o
>  obj-$(CONFIG_IMX_SCU)          += imx-scu.o misc.o imx-scu-irq.o
>  obj-$(CONFIG_IMX_SCU_PD)       += scu-pd.o
> diff --git a/drivers/firmware/imx/imx-dsp.c b/drivers/firmware/imx/imx-dsp.c
> new file mode 100644
> index 000000000000..a43d2db5cbdb
> --- /dev/null
> +++ b/drivers/firmware/imx/imx-dsp.c
> @@ -0,0 +1,155 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright 2019 NXP
> + *  Author: Daniel Baluta <daniel.baluta@nxp.com>
> + *
> + * Implementation of the DSP IPC interface (host side)
> + */
> +
> +#include <linux/firmware/imx/dsp.h>
> +#include <linux/kernel.h>
> +#include <linux/mailbox_client.h>
> +#include <linux/module.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +
> +/*
> + * imx_dsp_ring_doorbell - triggers an interrupt on the other side (DSP)
> + *
> + * @dsp: DSP IPC handle
> + * @chan_idx: index of the channel where to trigger the interrupt
> + *
> + * Returns non-negative value for success, negative value for error
> + */
> +int imx_dsp_ring_doorbell(struct imx_dsp_ipc *ipc, unsigned int idx)
> +{
> +       int ret;
> +       struct imx_dsp_chan *dsp_chan;
> +
> +       if (idx >= DSP_MU_CHAN_NUM)
> +               return -EINVAL;
> +
> +       dsp_chan = &ipc->chans[idx];
> +       ret = mbox_send_message(dsp_chan->ch, NULL);
> +       if (ret < 0)
> +               return ret;
> +
> +       return 0;
> +}
> +EXPORT_SYMBOL(imx_dsp_ring_doorbell);
> +
> +/*
> + * imx_dsp_handle_rx - rx callback used by imx mailbox
> + *
> + * @c: mbox client
> + * @msg: message received
> + *
> + * Users of DSP IPC will need to privde handle_reply and handle_request
> + * callbacks.
> + */
> +static void imx_dsp_handle_rx(struct mbox_client *c, void *msg)
> +{
> +       struct imx_dsp_chan *chan = container_of(c, struct imx_dsp_chan, cl);
> +
> +       if (chan->idx == 0) {
> +               chan->ipc->ops->handle_reply(chan->ipc);
> +       } else {
> +               chan->ipc->ops->handle_request(chan->ipc);
> +               imx_dsp_ring_doorbell(chan->ipc, 1);
> +       }
> +}
> +
> +static int imx_dsp_probe(struct platform_device *pdev)
> +{
> +       struct device *dev = &pdev->dev;
> +       struct imx_dsp_ipc *dsp_ipc;
> +       struct imx_dsp_chan *dsp_chan;
> +       struct mbox_client *cl;
> +       char *chan_name;
> +       int ret;
> +       int i, j;
> +
> +       device_set_of_node_from_dev(&pdev->dev, pdev->dev.parent);
> +
> +       dsp_ipc = devm_kzalloc(dev, sizeof(*dsp_ipc), GFP_KERNEL);
> +       if (!dsp_ipc)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < DSP_MU_CHAN_NUM; i++) {
> +               if (i < 2)
> +                       chan_name = kasprintf(GFP_KERNEL, "txdb%d", i);
> +               else
> +                       chan_name = kasprintf(GFP_KERNEL, "rxdb%d", i - 2);
> +
> +               if (!chan_name)
> +                       return -ENOMEM;
> +
> +               dsp_chan = &dsp_ipc->chans[i];
> +               cl = &dsp_chan->cl;
> +               cl->dev = dev;
> +               cl->tx_block = false;
> +               cl->knows_txdone = true;
> +               cl->rx_callback = imx_dsp_handle_rx;
> +
> +               dsp_chan->ipc = dsp_ipc;
> +               dsp_chan->idx = i % 2;
> +               dsp_chan->ch = mbox_request_channel_byname(cl, chan_name);
> +               if (IS_ERR(dsp_chan->ch)) {
> +                       ret = PTR_ERR(dsp_chan->ch);
> +                       if (ret != -EPROBE_DEFER)
> +                               dev_err(dev, "Failed to request mbox chan %s ret %d\n",
> +                                       chan_name, ret);
> +                       goto out;
> +               }
> +
> +               dev_dbg(dev, "request mbox chan %s\n", chan_name);
> +               /* chan_name is not used anymore by framework */
> +               kfree(chan_name);
> +       }
> +
> +       dsp_ipc->dev = dev;
> +
> +       dev_set_drvdata(dev, dsp_ipc);
> +
> +       dev_info(dev, "NXP i.MX DSP IPC initialized\n");
> +
> +       return devm_of_platform_populate(dev);
> +out:
> +       kfree(chan_name);
> +       for (j = 0; j < i; j++) {
> +               dsp_chan = &dsp_ipc->chans[j];
> +               mbox_free_channel(dsp_chan->ch);
> +       }
> +
> +       return ret;
> +}
> +
> +static int imx_dsp_remove(struct platform_device *pdev)
> +{
> +       struct imx_dsp_chan *dsp_chan;
> +       struct imx_dsp_ipc *dsp_ipc;
> +       int i;
> +
> +       dsp_ipc = dev_get_drvdata(&pdev->dev);
> +
> +       for (i = 0; i < DSP_MU_CHAN_NUM; i++) {
> +               dsp_chan = &dsp_ipc->chans[i];
> +               mbox_free_channel(dsp_chan->ch);
> +       }
> +
> +       return 0;
> +}
> +
> +static struct platform_driver imx_dsp_driver = {
> +       .driver = {
> +               .name = "imx-dsp",
> +       },
> +       .probe = imx_dsp_probe,
> +       .remove = imx_dsp_remove,
> +};
> +builtin_platform_driver(imx_dsp_driver);
> +
> +MODULE_AUTHOR("Daniel Baluta <daniel.baluta@nxp.com>");
> +MODULE_DESCRIPTION("IMX DSP IPC protocol driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/firmware/imx/dsp.h b/include/linux/firmware/imx/dsp.h
> new file mode 100644
> index 000000000000..7562099c9e46
> --- /dev/null
> +++ b/include/linux/firmware/imx/dsp.h
> @@ -0,0 +1,67 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * Copyright 2019 NXP
> + *
> + * Header file for the DSP IPC implementation
> + */
> +
> +#ifndef _IMX_DSP_IPC_H
> +#define _IMX_DSP_IPC_H
> +
> +#include <linux/device.h>
> +#include <linux/types.h>
> +#include <linux/mailbox_client.h>
> +
> +#define DSP_MU_CHAN_NUM                4
> +
> +struct imx_dsp_chan {
> +       struct imx_dsp_ipc *ipc;
> +       struct mbox_client cl;
> +       struct mbox_chan *ch;
> +       char *name;
> +       int idx;
> +};
> +
> +struct imx_dsp_ops {
> +       void (*handle_reply)(struct imx_dsp_ipc *ipc);
> +       void (*handle_request)(struct imx_dsp_ipc *ipc);
> +};
> +
> +struct imx_dsp_ipc {
> +       /* Host <-> DSP communication uses 2 txdb and 2 rxdb channels */
> +       struct imx_dsp_chan chans[DSP_MU_CHAN_NUM];
> +       struct device *dev;
> +       struct imx_dsp_ops *ops;
> +       void *private_data;
> +};
> +
> +static inline void imx_dsp_set_data(struct imx_dsp_ipc *ipc, void *data)
> +{
> +       if (!ipc)
> +               return;
> +
> +       ipc->private_data = data;
> +}
> +
> +static inline void *imx_dsp_get_data(struct imx_dsp_ipc *ipc)
> +{
> +       if (!ipc)
> +               return NULL;
> +
> +       return ipc->private_data;
> +}
> +
> +#if IS_ENABLED(CONFIG_IMX_DSP)
> +
> +int imx_dsp_ring_doorbell(struct imx_dsp_ipc *dsp, unsigned int chan_idx);
> +
> +#else
> +
> +static inline int imx_dsp_ring_doorbell(struct imx_dsp_ipc *ipc,
> +                                       unsigned int chan_idx)
> +{
> +       return -ENOTSUPP;
> +}
> +
> +#endif
> +#endif /* _IMX_DSP_IPC_H */
> --
> 2.17.1
>

Re: [PATCH v4] firmware: imx: Add DSP IPC protocol interface

[Shawn Guo]

On Thu, Aug 01, 2019 at 12:56:36PM +0300, Daniel Baluta wrote:
> Some of i.MX8 processors (e.g i.MX8QM, i.MX8QXP) contain
> the Tensilica HiFi4 DSP for advanced pre- and post-audio
> processing.
> 
> The communication between Host CPU and DSP firmware is
> taking place using a shared memory area for message passing
> and a dedicated Messaging Unit for notifications.
> 
> DSP IPC protocol offers a doorbell interface using
> imx-mailbox API.
> 
> We use 4 MU channels (2 x TXDB, 2 x RXDB) to implement a
> request-reply protocol.
> 
> Connection 0 (txdb0, rxdb0):
>         - Host writes messasge to shared memory [SHMEM]
> 	- Host sends a request [MU]
> 	- DSP handles request [SHMEM]
> 	- DSP sends reply [MU]
> 
> Connection 1 (txdb1, rxdb1):
> 	- DSP writes a message to shared memory [SHMEM]
> 	- DSP sends a request [MU]
> 	- Host handles request [SHMEM]
> 	- Host sends reply [MU]
> 
> The protocol interface will be used by a Host client to
> communicate with the DSP. First client will be the i.MX8
> part from Sound Open Firmware infrastructure.
> 
> The protocol offers the following interface:
> 
> On Tx:
>    - imx_dsp_ring_doorbell, will be called to notify the DSP
>    that it needs to handle a request.
> 
> On Rx:
>    - clients need to provide two callbacks:
> 	.handle_reply
> 	.handle_request
>   - the callbacks will be used by the protocol on
>     notification arrival from DSP.
> 
> Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>

Applied, thanks.