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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 | { | |
54 | struct demo_client *dc = container_of(mbox_client, | |
55 | struct demo_client, cl); | |
70c03634 | 56 | if (dc->async) { |
15320fbc JB |
57 | if (is_an_ack(mssg)) { |
58 | /* An ACK to our last sample sent */ | |
59 | return; /* Or do something else here */ | |
60 | } else { /* A new message from remote */ | |
61 | queue_req(mssg); | |
62 | } | |
63 | } else { | |
64 | /* Remote f/w sends only ACK packets on this channel */ | |
65 | return; | |
66 | } | |
67 | } | |
68 | ||
69 | static void sample_sent(struct mbox_client *cl, void *mssg, int r) | |
70 | { | |
71 | struct demo_client *dc = container_of(mbox_client, | |
72 | struct demo_client, cl); | |
73 | complete(&dc->c); | |
74 | } | |
75 | ||
76 | static void client_demo(struct platform_device *pdev) | |
77 | { | |
78 | struct demo_client *dc_sync, *dc_async; | |
79 | /* The controller already knows async_pkt and sync_pkt */ | |
80 | struct async_pkt ap; | |
81 | struct sync_pkt sp; | |
82 | ||
83 | dc_sync = kzalloc(sizeof(*dc_sync), GFP_KERNEL); | |
84 | dc_async = kzalloc(sizeof(*dc_async), GFP_KERNEL); | |
85 | ||
86 | /* Populate non-blocking mode client */ | |
87 | dc_async->cl.dev = &pdev->dev; | |
88 | dc_async->cl.rx_callback = message_from_remote; | |
89 | dc_async->cl.tx_done = sample_sent; | |
90 | dc_async->cl.tx_block = false; | |
91 | dc_async->cl.tx_tout = 0; /* doesn't matter here */ | |
92 | dc_async->cl.knows_txdone = false; /* depending upon protocol */ | |
93 | dc_async->async = true; | |
94 | init_completion(&dc_async->c); | |
95 | ||
96 | /* Populate blocking mode client */ | |
97 | dc_sync->cl.dev = &pdev->dev; | |
98 | dc_sync->cl.rx_callback = message_from_remote; | |
99 | dc_sync->cl.tx_done = NULL; /* operate in blocking mode */ | |
100 | dc_sync->cl.tx_block = true; | |
101 | dc_sync->cl.tx_tout = 500; /* by half a second */ | |
102 | dc_sync->cl.knows_txdone = false; /* depending upon protocol */ | |
103 | dc_sync->async = false; | |
104 | ||
105 | /* ASync mailbox is listed second in 'mboxes' property */ | |
106 | dc_async->mbox = mbox_request_channel(&dc_async->cl, 1); | |
107 | /* Populate data packet */ | |
108 | /* ap.xxx = 123; etc */ | |
109 | /* Send async message to remote */ | |
110 | mbox_send_message(dc_async->mbox, &ap); | |
111 | ||
112 | /* Sync mailbox is listed first in 'mboxes' property */ | |
113 | dc_sync->mbox = mbox_request_channel(&dc_sync->cl, 0); | |
114 | /* Populate data packet */ | |
115 | /* sp.abc = 123; etc */ | |
116 | /* Send message to remote in blocking mode */ | |
117 | mbox_send_message(dc_sync->mbox, &sp); | |
118 | /* At this point 'sp' has been sent */ | |
119 | ||
120 | /* Now wait for async chan to be done */ | |
121 | wait_for_completion(&dc_async->c); | |
122 | } |