上篇介绍了电源管理入门-4子系统reset提到子系统reset的执行为了安全可以到SCP里面去执行但是怎么把这个消息传递过去呢答案就是mailbox。Mailbox是核间通信软硬件的统称。在软件上可以使用SCMI协议共享内存报文头在硬件上可以使用PL320或者MHU。1. 整体架构介绍Reset系统架构框图上图以NPU子模块的服务为例子Mailbox的硬件使用PL320整体流程如下Reset consumer模块执行devm_reset_control_get获取npu_reset复位句柄然后通过reset_control_reset触发复位Linux系统reset framework找到复位驱动并执行ops-reset回调函数scmi-reset驱动里面提供.reset函数的实现scmi_reset_deassert并执行arm-scmi里面提供scmi reset协议的实现模块reset里面提供reset函数scmi_reset_domain_resetarm-scmi里面提供scmi协议收发的框架driver提供do_xferarm-scmi里面提供mailbox的接口函数mailbox_send_messagearm-scmi里面提供共享内存的操作函数shmem_tx_preparemailbox驱动里面提供硬件PL320的寄存器操作实现pl320_mbox_send_dataSCP中PL320驱动模块接收mailbox中断SCP中SMT模块从共享内存中读取SCMI报文数据SCP中SCMI模块对SCMI协议报文进行解析并进行分发处理SCP中SCMI RESET DOMAIN协议模块对报文进行功能处理SCP中RESET DOMAIN模块屏蔽硬件差异实现统一APISCP中JUNO RESET DOMAIN模块提供具体硬件CRU寄存器操作实现2 Linux中reset模块2.1 Reset consumer之前的文章电源管理入门-4子系统reset介绍了怎么使用Linux的reset子系统这里我们就直接使用需要在DTS中修改即可。reset使用Linux自带的reset框架假定consumer-firmware-npu这个驱动要使用NPU的reset定义在DTS中有reset consumer的说明consumer-firmware-npu。/{consumer_firmware0x0{compatibleconsumer-firmware-npu;reg0x0 0x0 0x0 0x00;resetsscmi_reset0;reset-namesnpu_reset;};};drivers/firmware/consumer/consumer.c中驱动需要使用reset功能。static struct platform_driver consumer_firmware_driver{.driver{.nameconsumer_firmware, .of_match_tableconsumer_firmware_of_match,}, .probeconsumer_firmware_probe, .removeconsumer_firmware_remove,};consumer_firmware_probe --》devm_reset_control_get //获取npu_reset复位句柄 --》consumer_fw_firmware_cb --》consumer_fw_memcpy //拷贝镜像 --》consumer_control_reset //通知reset驱动进行reset这样DTS探测到consumer_firmware的时候就会触发reset操作。reset_control_reset rstc-rcdev-ops-reset(rstc-rcdev, rstc-id);reset的provider驱动使用compatible “scmi-reset”;驱动详细见后面2.2reset provider中分析。当reset时在drivers/reset/reset-scmi.c中实现static int scmi_reset_reset(struct reset_controller_dev *rcdev, unsigned longid){const struct scmi_protocol_handle *phto_scmi_handle(rcdev);returnreset_ops-reset(ph,id);}static const struct reset_control_ops scmi_reset_ops{.assertscmi_reset_assert, .deassertscmi_reset_deassert, .resetscmi_reset_reset,};reset_ops在scmi_reset_probe的时候会赋值reset_opshandle-devm_protocol_get(sdev, SCMI_PROTOCOL_RESET,ph);handle-devm_protocol_get为drivers/firmware/arm_scmi/driver.c中scmi_devm_protocol_getpiscmi_get_protocol_instance(handle, protocol_id);returnpi-proto-ops;在scmi协议初始化的时候scmi_reset_register会注册0x16的回调函数详细分析见2.2.1SCMI reset协议初始化内容。在drivers/firmware/arm_scmi/reset.c中static const struct scmi_reset_proto_ops reset_proto_ops{.num_domains_getscmi_reset_num_domains_get, .name_getscmi_reset_name_get, .latency_getscmi_reset_latency_get, .resetscmi_reset_domain_reset, .assertscmi_reset_domain_assert, .deassertscmi_reset_domain_deassert,};scmi_reset_domain_reset–》scmi_domain_reset ret ph-xops-do_xfer(ph, t); do_xfer在drivers/firmware/arm_scmi/driver.c中实现do_xfer(ph, xfer);retinfo-desc-ops-send_message(cinfo, xfer);send_message在drivers/firmware/arm_scmi/mailbox.c中定义static const struct scmi_transport_ops scmi_mailbox_ops{.chan_availablemailbox_chan_available, .chan_setupmailbox_chan_setup, .chan_freemailbox_chan_free, .send_messagemailbox_send_message, .mark_txdonemailbox_mark_txdone, .fetch_responsemailbox_fetch_response, .fetch_notificationmailbox_fetch_notification, .clear_channelmailbox_clear_channel, .poll_donemailbox_poll_done,};mailbox_send_message见3.2中分析2.2 Reset providerreset的provider是scmi-reset驱动DTS中设置如下scmi_reset: protocol16{reg0x16;#reset-cells 1;};代码位置在drivers/reset/reset-scmi.cstatic struct scmi_driver scmi_reset_driver{.namescmi-reset, .probescmi_reset_probe, .id_tablescmi_id_table,};module_scmi_driver(scmi_reset_driver);scmi_reset_probe的定义如下static int scmi_reset_probe(struct scmi_device *sdev){reset_opshandle-devm_protocol_get(sdev, SCMI_PROTOCOL_RESET,ph);datadevm_kzalloc(dev, sizeof(*data), GFP_KERNEL);>rcdev.opsscmi_reset_ops;>rcdev.ownerTHIS_MODULE;>rcdev.of_nodenp;>rcdev.nr_resetsreset_ops-num_domains_get(ph);>phph;returndevm_reset_controller_register(dev,data-rcdev);//进行驱动注册}handle-devm_protocol_get为scmi_devm_protocol_get这里面发送了三条0x16的scmi消息 scmi_devm_protocol_get-scmi_get_protocol_instancescmi_get_protocol_instance里面发送了三条0x16的scmi消息来获取reset的版本号支持那些devices等信息3. Linux SCMI reset通信如上图中Linux通过非安全通道跟SCP交互。3.1 SCMI reset协议初始化系统初始化的时候会执行subsys_initcall(scmi_driver_init);在drivers/firmware/arm_scmi/driver.c中static int __init scmi_driver_init(void){int ret;/* Bail outifno SCMI transport was configured */if(WARN_ON(!IS_ENABLED(CONFIG_ARM_SCMI_HAVE_TRANSPORT)))return-EINVAL;scmi_bus_init();/* Initialize any compiled-in transportwhichprovided an init/exit */ retscmi_transports_init();if(ret)returnret;scmi_base_register();scmi_clock_register();scmi_perf_register();scmi_power_register();scmi_reset_register();scmi_sensors_register();scmi_voltage_register();scmi_system_register();returnplatform_driver_register(scmi_driver);}scmi_driver的定义为static struct platform_driver scmi_driver{.driver{.namearm-scmi, .suppress_bind_attrstrue, .of_match_tablescmi_of_match, .dev_groupsversions_groups,}, .probescmi_probe, .removescmi_remove,};drivers/firmware/arm_scmi/driver.c中scmi_probe函数static int scmi_probe(struct platform_device *pdev){retscmi_txrx_setup(info, dev, SCMI_PROTOCOL_BASE);retscmi_xfer_info_init(info);、 retscmi_protocol_acquire(handle, SCMI_PROTOCOL_BASE);scmi_txrx_setup中会调用mailbox_chan_setup函数sizeresource_size(res);smbox-shmemdevm_ioremap(dev, res.start, size);smbox-chanmbox_request_channel(cl, tx ?0:1);scmi_protocol_acquire函数int scmi_protocol_acquire(const struct scmi_handle *handle, u8 protocol_id){returnPTR_ERR_OR_ZERO(scmi_get_protocol_instance(handle, protocol_id));}scmi_get_protocol_instance scmi_alloc_init_protocol_instance(info, proto);retpi-proto-instance_init(pi-ph);drivers/firmware/arm_scmi/base.c中定义了instance_initstatic int scmi_base_protocol_init(const struct scmi_protocol_handle *ph)retph-xops-version_get(ph,version);static const struct scmi_xfer_ops xfer_ops{.version_getversion_get, .xfer_get_initxfer_get_init, .reset_rx_to_maxszreset_rx_to_maxsz, .do_xferdo_xfer, .do_xfer_with_responsedo_xfer_with_response, .xfer_putxfer_put,};version_get中进行scmi的发送static int version_get(const struct scmi_protocol_handle *ph, u32 *version){retxfer_get_init(ph, PROTOCOL_VERSION,0, sizeof(*version),t);retdo_xfer(ph, t);xfer_put(ph, t);xfer_get_init中进行了赋值xfer-hdr.id msg_id; do_xfer进行了发送操作之后等待回复retinfo-desc-ops-send_message(cinfo, xfer);/* And wewaitforthe response. */timeoutmsecs_to_jiffies(info-desc-max_rx_timeout_ms);if(!wait_for_completion_timeout(xfer-done,timeout)){dev_err(dev,timed out in resp(caller: %pS)\n,(void *)_RET_IP_);ret-ETIMEDOUT;}send_message在drivers/firmware/arm_scmi/mailbox.c中定义static const struct scmi_transport_ops scmi_mailbox_ops{.chan_availablemailbox_chan_available, .chan_setupmailbox_chan_setup, .chan_freemailbox_chan_free, .send_messagemailbox_send_message, .mark_txdonemailbox_mark_txdone, .fetch_responsemailbox_fetch_response, .fetch_notificationmailbox_fetch_notification, .clear_channelmailbox_clear_channel, .poll_donemailbox_poll_done,};mbox_send_message就是mailbox提供的发消息接口函数详细介绍见3.2中初始化的时候不仅初始化了scmi协议还调用了scmi_reset_register();注册了0x16的scmi reset协议 在drivers/firmware/arm_scmi/reset.c中static const struct scmi_protocol scmi_reset{.idSCMI_PROTOCOL_RESET, .ownerTHIS_MODULE, .instance_initscmi_reset_protocol_init, .opsreset_proto_ops, .eventsreset_protocol_events,};DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(reset, scmi_reset)#define DEFINE_SCMI_PROTOCOL_REGISTER_UNREGISTER(name, proto) \static const struct scmi_protocol *__this_proto(proto);\\int __init scmi_##name##_register(void) \{\returnscmi_protocol_register(__this_proto);\}3.2 SCMI reset消息收发A核先往某个指定共享内存空间buffer写数据然后写入共享内存空间的地址信息到相应通道数据寄存器mailbox触发中断给R核;M核SCP通过得到mailbox中断获取共享内存相应offset读取buffer数据M核SCP通过mailbox触发中断通知A核接收消息完毕。PL320和MHU硬件的区别PL320带传输数据和中断功能但是数据量比较小7*32bit。对于新的SoC来说数据传输基本都使用共享内存PL320自带的数据传输基本用不上了所以其算过时了。新的MHU只保留了中断功能并且是1对1的集成核间通信时成对出现用几个加几个更加的灵活PL320是一次32个通道集成进SoC的也可能浪费。我们以PL320为例只使用其中断数据还是通过共享内存传输驱动跟MHU原理差不多。关于PL320可以参考ARM官网的文档后面会专门写一个核间通信的专题介绍下。在drivers/mailbox/mailbox.c中mailbox_send_message发消息的时候会调用mbox_send_messagemailbox_send_message --》mbox_send_message --》msg_submit static void msg_submit(struct mbox_chan *chan){datachan-msg_data[idx];if(chan-cl-tx_prepare)chan-cl-tx_prepare(chan-cl, data);errchan-mbox-ops-send_data(chan, data);}tx_prepare-》shmem_tx_prepare会往共享内存里面存入数据在drivers/firmware/arm_scmi/shmem.c中void shmem_tx_prepare(struct scmi_shared_mem __iomem *shmem, struct scmi_xfer *xfer){spin_until_cond(ioread32(shmem-channel_status)SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE);iowrite32(0x0,shmem-channel_status);iowrite32(xfer-hdr.poll_completion ?0:SCMI_SHMEM_FLAG_INTR_ENABLED,shmem-flags);iowrite32(sizeof(shmem-msg_header) xfer-tx.len,shmem-length);iowrite32(pack_scmi_header(xfer-hdr),shmem-msg_header);pr_info(#### shmem_tx_prepare shmem-msg_header0x%x\n, shmem-msg_header);if(xfer-tx.buf){memcpy_toio(shmem-msg_payload, xfer-tx.buf, xfer-tx.len);pr_info(#### shmem_tx_prepare shmem-msg_payload[0]0x%x\n,(int)shmem-msg_payload[0]);}}发消息drivers/mailbox/pl320-ipc.c中pl320_mbox_send_data函数static const struct mbox_chan_ops pl320_mbox_ops{.send_datapl320_mbox_send_data,};ops-send_data-》pl320_mbox_send_data-》__ipc_send(pl320_id, ch, buf);会触发中断static void __ipc_send(int pl320_id, int mbox, u32 *data){ipc_baseget_ipc_base(pl320_id);for(i0;iMBOX_MSG_LEN;i)writel_relaxed(data[i], ipc_base IPCMxDR(mbox, i));if(mbox %20)writel_relaxed(0x1, ipc_base IPCMxSEND(mbox));elsewritel_relaxed(0x2, ipc_base IPCMxSEND(mbox));}收消息drivers/mailbox/pl320-ipc.c中ipc_handlerfor(idx0;idxMBOX_CHAN_MAX;idx)if(irq_stat(1idx))receive_flag|channel_handler(mbox, idx);channel_handler中会清中断4. SCP中reset4.1 固件新增module根据我们的需求需要处理0x16 scmi reset domain协议所以在scmi module之后需要新加协议层scmi-reset-domain根据SCP固件的分层结构协议层之后需要添加HAL层和驱动层综上需要在product/juno/scp_ramfw/CMakeLists.txt中新加如下module模块if(SCP_ENABLE_SCMI_RESET)target_sources(juno-bl2 PRIVATE${CMAKE_CURRENT_SOURCE_DIR}/config_reset_domain.c${CMAKE_CURRENT_SOURCE_DIR}/config_scmi_reset_domain.c${CMAKE_CURRENT_SOURCE_DIR}/config_juno_reset_domain.c)endif()if(SCP_ENABLE_SCMI_RESET)list(APPEND SCP_MODULESreset-domain)list(APPEND SCP_MODULESscmi-reset-domain)list(APPEND SCP_MODULESjuno-reset-domain)endif()打开SCP_ENABLE_SCMI_RESET宏在product/juno/scp_ramfw/Firmware.cmake中 set(SCP_ENABLE_SCMI_RESET TRUE) set(SCP_ENABLE_SCMI_RESET_INIT TRUE)4.2 scmi_reset_domain初始化新增scmi_reset_domain协议module后首先初始化的时候需要向scmi注册这样当收到scmi消息的时候会根据scmi协议号0x16进行协议分发处理。module/scmi_reset_domain/src/mod_scmi_reset_domain.c中初始化会执行.bind scmi_reset_bind,函数statusfwk_module_bind(FWK_ID_MODULE(FWK_MODULE_IDX_SCMI), FWK_ID_API(FWK_MODULE_IDX_SCMI, MOD_SCMI_API_IDX_PROTOCOL),scmi_rd_ctx.scmi_api);去绑定scmi模块在scmi中执行.process_bind_request scmi_process_bind_request,scmi_ctx.protocol_table[PROTOCOL_TABLE_RESERVED_ENTRIES_COUNT scmi_ctx.protocol_count].idsource_id;*apiscmi_from_protocol_api;会填充scmi_ctx.protocol_table之后.bind scmi_bind,执行for(protocol_idx0;protocol_idxscmi_ctx.protocol_count;protocol_idx){protocolscmi_ctx.protocol_table[PROTOCOL_TABLE_RESERVED_ENTRIES_COUNT protocol_idx];//根据module信息进行绑定拿到api statusfwk_module_bind(protocol-id, FWK_ID_API(fwk_id_get_module_idx(protocol-id),0),protocol_api);//使用拿到的api获取scmi协议id号 statusprotocol_api-get_scmi_protocol_id(protocol-id,scmi_protocol_id);FWK_LOG_INFO([SCMI] Support scmi_protocol_id:0x%x, scmi_protocol_id));scmi_ctx.scmi_protocol_id_to_idx[scmi_protocol_id](uint8_t)(protocol_idx PROTOCOL_TABLE_RESERVED_ENTRIES_COUNT);protocol-message_handlerprotocol_api-message_handler;}protocol 是scmi协议的module首先绑定这个module拿到两个apistatic struct mod_scmi_to_protocol_api scmi_reset_mod_scmi_to_protocol_api{.get_scmi_protocol_idscmi_reset_get_scmi_protocol_id, .message_handlerscmi_reset_message_handler};scmi_reset_get_scmi_protocol_id为获取协议id /*!*\brief SCMI Reset Domain Protocol */#define MOD_SCMI_PROTOCOL_ID_RESET_DOMAIN UINT32_C(0x16)static int scmi_reset_get_scmi_protocol_id(fwk_id_t protocol_id, uint8_t *scmi_protocol_id){*scmi_protocol_idMOD_SCMI_PROTOCOL_ID_RESET_DOMAIN;returnFWK_SUCCESS;}4.3 scmi_reset_domain消息处理协议模块负责处理reset相关的所有协议子命令对于scmi_reset_domain一共支持6个子命令如下enum scmi_command_id{MOD_SCMI_PROTOCOL_VERSION0x000, MOD_SCMI_PROTOCOL_ATTRIBUTES0x001, MOD_SCMI_PROTOCOL_MESSAGE_ATTRIBUTES0x002};enum scmi_reset_domain_command_id{MOD_SCMI_RESET_DOMAIN_ATTRIBUTES0x03, MOD_SCMI_RESET_REQUEST0x04, MOD_SCMI_RESET_NOTIFY0x05, MOD_SCMI_RESET_COMMAND_COUNT,};我们需要在协议模块scmi_reset_domain中给这些命令设计处理函数如下static int(*msg_handler_table[])(fwk_id_t, const uint32_t *){[MOD_SCMI_PROTOCOL_VERSION]protocol_version_handler,[MOD_SCMI_PROTOCOL_ATTRIBUTES]protocol_attributes_handler,[MOD_SCMI_PROTOCOL_MESSAGE_ATTRIBUTES]protocol_message_attributes_handler,[MOD_SCMI_RESET_DOMAIN_ATTRIBUTES]reset_attributes_handler,[MOD_SCMI_RESET_REQUEST]reset_request_handler,#ifdef BUILD_HAS_SCMI_NOTIFICATIONS[MOD_SCMI_RESET_NOTIFY]reset_notify_handler,#endif};我们以为reset_request_handler例进行说明4.3.1 scmi_reset_domain中处理static struct mod_scmi_to_protocol_api scmi_reset_mod_scmi_to_protocol_api{.get_scmi_protocol_idscmi_reset_get_scmi_protocol_id, .message_handlerscmi_reset_message_handler};scmi_reset_message_handler函数中会根据命令id找到处理函数执行 msg_handler_table[message_id](service_id, payload); message_id就是cmd idpayload就是协议携带的数据部分。[MOD_SCMI_RESET_REQUEST]reset_request_handler,reset_request_handler中会解析payload并对payload的数据大小进行校验然后进行解析struct scmi_reset_domain_request_a2p{uint32_t domain_id;uint32_t flags;uint32_t reset_state;};params*(const struct scmi_reset_domain_request_a2p *)payload;statusget_reset_device(service_id, params.domain_id,reset_device);statusscmi_reset_domain_reset_request_policy(policy_status,mode,reset_state, agent_id, params.domain_id);statusreset_api-set_reset_state(reset_device-element_id, mode, reset_state,(uintptr_t)agent_id);reset_api-set_reset_state是从HAL层拿到的api4.3.2 reset-domain HAL层/* HAL API */ static const struct mod_reset_domain_drv_api reset_api{.set_reset_stateset_reset_state,};static int set_reset_state(fwk_id_t reset_dev_id, enum mod_reset_domain_mode mode, uint32_t reset_state, uintptr_t cookie){struct rd_dev_ctx *reset_ctx;unsigned int reset_domain_idxfwk_id_get_element_idx(reset_dev_id);FWK_LOG_INFO([RESET DOMAIN] set_reset_state);reset_ctxmodule_reset_ctx.dev_ctx_table[reset_domain_idx];returnreset_ctx-driver_api-set_reset_state(reset_ctx-config-driver_id, mode, reset_state, cookie);}从driver层拿到api进行处理4.3.3 juno-reset-domain驱动层static struct mod_reset_domain_drv_api juno_reset_domain_drv_api{.set_reset_statejuno_set_reset_state,};static int juno_set_reset_state(fwk_id_t dev_id, enum mod_reset_domain_mode mode, uint32_t reset_state, uintptr_t cookie){unsigned int domain_idxfwk_id_get_element_idx(dev_id);dev_ctxmodule_juno_reset_ctx.dev_ctx_table[domain_idx];if(domain_idxjuno_RESET_DOMAIN_IDX_NPU){statushandle_dev_reset_set_state(dev_ctx);if(status!FWK_SUCCESS){returnstatus;}}returnFWK_SUCCESS;}handle_dev_reset_set_state里面处理具体的硬件寄存器操作/* Helper functions */ static int handle_dev_reset_set_state(struct juno_reset_dev_ctx *dev_ctx){/* Reset device */ dev_ctx-reset_stateDEVICE_STATE_RESET;*dev_config-reset_reg0;for(int j0;j10000;j);*dev_config-reset_reg1;*dev_config-clkctl_reg1;dev_ctx-reset_stateDEVICE_STATE_NORMAL;根据2.4章节中CRU硬件这里需要对reset寄存器和clk寄存器进行写操作来实现其他硬件模块的reset功能。5. 硬件CRU设计CRUClock Reset Unit位于SCP子系统中受SCP软件控制然后硬件信号会连接到其他子系统上我们的SCP固件一般运行在ARM的M核心上还有一堆外围的器件例如NXP的imx8qm里面**将clock gate信号和reset信号送给多个子系统有时钟控制、reset控制等需求的子系统。通过SCP软件来操作CRU的相关寄存器从而实现对子系统时钟和复位信号的控制芯片手册会给出控制CRU的reset及clk的寄存器配置操作响应的寄存器即可。后记本小节介绍比较详细其实很多知识点都是相通的例如SCMI、SCP、Mailbox、DTS这些东西早晚都需要掌握但是通过一个业务流程或者场景就可以学习到本文就是一个了解这些知识的机会。“啥都懂一点啥都不精通干啥都能干干啥啥不是专业入门劝退堪称程序员杂家”。后续会继续更新纯干货分析欢迎分享给朋友欢迎评论交流公众号“那路谈OS与SoC嵌入式软件”欢迎关注个人文章汇总https://thatway1989.github.io