| Kyle Swenson | 8d8f654 | 2021-03-15 11:02:55 -0600 | [diff] [blame] | 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 | } |