[mirror_ubuntu-bionic-kernel.git] / Documentation / mailbox.txt

		The Common Mailbox Framework
		Jassi Brar <jaswinder.singh@linaro.org>

 This document aims to help developers write client and controller
drivers for the API. But before we start, let us note that the
client (especially) and controller drivers are likely going to be
very platform specific because the remote firmware is likely to be
proprietary and implement non-standard protocol. So even if two
platforms employ, say, PL320 controller, the client drivers can't
be shared across them. Even the PL320 driver might need to accommodate
some platform specific quirks. So the API is meant mainly to avoid
similar copies of code written for each platform. Having said that,
nothing prevents the remote f/w to also be Linux based and use the
same api there. However none of that helps us locally because we only
ever deal at client's protocol level.
 Some of the choices made during implementation are the result of this
peculiarity of this "common" framework.


	Part 1 - Controller Driver (See include/linux/mailbox_controller.h)

 Allocate mbox_controller and the array of mbox_chan.
Populate mbox_chan_ops, except peek_data() all are mandatory.
The controller driver might know a message has been consumed
by the remote by getting an IRQ or polling some hardware flag
or it can never know (the client knows by way of the protocol).
The method in order of preference is IRQ -> Poll -> None, which
the controller driver should set via 'txdone_irq' or 'txdone_poll'
or neither.


	Part 2 - Client Driver (See include/linux/mailbox_client.h)

 The client might want to operate in blocking mode (synchronously
send a message through before returning) or non-blocking/async mode (submit
a message and a callback function to the API and return immediately).


struct demo_client {
	struct mbox_client cl;
	struct mbox_chan *mbox;
	struct completion c;
	bool async;
	/* ... */
};

/*
 * This is the handler for data received from remote. The behaviour is purely
 * dependent upon the protocol. This is just an example.
 */
static void message_from_remote(struct mbox_client *cl, void *mssg)
{
	struct demo_client *dc = container_of(cl, struct demo_client, cl);
	if (dc->async) {
		if (is_an_ack(mssg)) {
			/* An ACK to our last sample sent */
			return; /* Or do something else here */
		} else { /* A new message from remote */
			queue_req(mssg);
		}
	} else {
		/* Remote f/w sends only ACK packets on this channel */
		return;
	}
}

static void sample_sent(struct mbox_client *cl, void *mssg, int r)
{
	struct demo_client *dc = container_of(cl, struct demo_client, cl);
	complete(&dc->c);
}

static void client_demo(struct platform_device *pdev)
{
	struct demo_client *dc_sync, *dc_async;
	/* The controller already knows async_pkt and sync_pkt */
	struct async_pkt ap;
	struct sync_pkt sp;

	dc_sync = kzalloc(sizeof(*dc_sync), GFP_KERNEL);
	dc_async = kzalloc(sizeof(*dc_async), GFP_KERNEL);

	/* Populate non-blocking mode client */
	dc_async->cl.dev = &pdev->dev;
	dc_async->cl.rx_callback = message_from_remote;
	dc_async->cl.tx_done = sample_sent;
	dc_async->cl.tx_block = false;
	dc_async->cl.tx_tout = 0; /* doesn't matter here */
	dc_async->cl.knows_txdone = false; /* depending upon protocol */
	dc_async->async = true;
	init_completion(&dc_async->c);

	/* Populate blocking mode client */
	dc_sync->cl.dev = &pdev->dev;
	dc_sync->cl.rx_callback = message_from_remote;
	dc_sync->cl.tx_done = NULL; /* operate in blocking mode */
	dc_sync->cl.tx_block = true;
	dc_sync->cl.tx_tout = 500; /* by half a second */
	dc_sync->cl.knows_txdone = false; /* depending upon protocol */
	dc_sync->async = false;

	/* ASync mailbox is listed second in 'mboxes' property */
	dc_async->mbox = mbox_request_channel(&dc_async->cl, 1);
	/* Populate data packet */
	/* ap.xxx = 123; etc */
	/* Send async message to remote */
	mbox_send_message(dc_async->mbox, &ap);

	/* Sync mailbox is listed first in 'mboxes' property */
	dc_sync->mbox = mbox_request_channel(&dc_sync->cl, 0);
	/* Populate data packet */
	/* sp.abc = 123; etc */
	/* Send message to remote in blocking mode */
	mbox_send_message(dc_sync->mbox, &sp);
	/* At this point 'sp' has been sent */

	/* Now wait for async chan to be done */
	wait_for_completion(&dc_async->c);
}
Commit	Line	Data
15320fbc JB	1	The Common Mailbox Framework
	2	Jassi Brar <jaswinder.singh@linaro.org>
	3
	4	This document aims to help developers write client and controller
	5	drivers for the API. But before we start, let us note that the
	6	client (especially) and controller drivers are likely going to be
	7	very platform specific because the remote firmware is likely to be
	8	proprietary and implement non-standard protocol. So even if two
	9	platforms employ, say, PL320 controller, the client drivers can't
	10	be shared across them. Even the PL320 driver might need to accommodate
	11	some platform specific quirks. So the API is meant mainly to avoid
	12	similar copies of code written for each platform. Having said that,
	13	nothing prevents the remote f/w to also be Linux based and use the
	14	same api there. However none of that helps us locally because we only
	15	ever deal at client's protocol level.
	16	Some of the choices made during implementation are the result of this
	17	peculiarity of this "common" framework.
	18
	19
	20
	21	Part 1 - Controller Driver (See include/linux/mailbox_controller.h)
	22
	23	Allocate mbox_controller and the array of mbox_chan.
	24	Populate mbox_chan_ops, except peek_data() all are mandatory.
	25	The controller driver might know a message has been consumed
	26	by the remote by getting an IRQ or polling some hardware flag
	27	or it can never know (the client knows by way of the protocol).
	28	The method in order of preference is IRQ -> Poll -> None, which
	29	the controller driver should set via 'txdone_irq' or 'txdone_poll'
	30	or neither.
	31
	32
	33	Part 2 - Client Driver (See include/linux/mailbox_client.h)
	34
	35	The client might want to operate in blocking mode (synchronously
	36	send a message through before returning) or non-blocking/async mode (submit
	37	a message and a callback function to the API and return immediately).
	38
	39
	40	struct demo_client {
	41	struct mbox_client cl;
	42	struct mbox_chan *mbox;
	43	struct completion c;
	44	bool async;
	45	/* ... */
	46	};
	47
	48	/*
	49	* This is the handler for data received from remote. The behaviour is purely
	50	* dependent upon the protocol. This is just an example.
	51	*/
	52	static void message_from_remote(struct mbox_client cl, void mssg)
	53	{
7bbac697	54	struct demo_client *dc = container_of(cl, struct demo_client, cl);
70c03634	55	if (dc->async) {
15320fbc JB	56	if (is_an_ack(mssg)) {
	57	/* An ACK to our last sample sent */
	58	return; /* Or do something else here */
	59	} else { /* A new message from remote */
	60	queue_req(mssg);
	61	}
	62	} else {
	63	/* Remote f/w sends only ACK packets on this channel */
	64	return;
	65	}
	66	}
	67
	68	static void sample_sent(struct mbox_client cl, void mssg, int r)
	69	{
7bbac697	70	struct demo_client *dc = container_of(cl, struct demo_client, cl);
15320fbc JB	71	complete(&dc->c);
	72	}
	73
	74	static void client_demo(struct platform_device *pdev)
	75	{
	76	struct demo_client dc_sync, dc_async;
	77	/* The controller already knows async_pkt and sync_pkt */
	78	struct async_pkt ap;
	79	struct sync_pkt sp;
	80
	81	dc_sync = kzalloc(sizeof(*dc_sync), GFP_KERNEL);
	82	dc_async = kzalloc(sizeof(*dc_async), GFP_KERNEL);
	83
	84	/* Populate non-blocking mode client */
	85	dc_async->cl.dev = &pdev->dev;
	86	dc_async->cl.rx_callback = message_from_remote;
	87	dc_async->cl.tx_done = sample_sent;
	88	dc_async->cl.tx_block = false;
	89	dc_async->cl.tx_tout = 0; /* doesn't matter here */
	90	dc_async->cl.knows_txdone = false; /* depending upon protocol */
	91	dc_async->async = true;
	92	init_completion(&dc_async->c);
	93
	94	/* Populate blocking mode client */
	95	dc_sync->cl.dev = &pdev->dev;
	96	dc_sync->cl.rx_callback = message_from_remote;
	97	dc_sync->cl.tx_done = NULL; /* operate in blocking mode */
	98	dc_sync->cl.tx_block = true;
	99	dc_sync->cl.tx_tout = 500; /* by half a second */
	100	dc_sync->cl.knows_txdone = false; /* depending upon protocol */
	101	dc_sync->async = false;
	102
	103	/* ASync mailbox is listed second in 'mboxes' property */
	104	dc_async->mbox = mbox_request_channel(&dc_async->cl, 1);
	105	/* Populate data packet */
	106	/* ap.xxx = 123; etc */
	107	/* Send async message to remote */
	108	mbox_send_message(dc_async->mbox, &ap);
	109
	110	/* Sync mailbox is listed first in 'mboxes' property */
	111	dc_sync->mbox = mbox_request_channel(&dc_sync->cl, 0);
	112	/* Populate data packet */
	113	/* sp.abc = 123; etc */
	114	/* Send message to remote in blocking mode */
	115	mbox_send_message(dc_sync->mbox, &sp);
	116	/* At this point 'sp' has been sent */
	117
	118	/* Now wait for async chan to be done */
	119	wait_for_completion(&dc_async->c);
	120	}