blob: 7ed371c852046b3dd5d993db1815d00a9d8f4bc0
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 | { |
54 | struct demo_client *dc = container_of(cl, struct demo_client, cl); |
55 | if (dc->async) { |
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 | { |
70 | struct demo_client *dc = container_of(cl, struct demo_client, cl); |
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 | } |
121 |