MMC子系统调用过程浅析（Core层）

Core层关系图:

在Card层中，分析到调用mmc_start_req(card->host, areq, (int *) &status)来处理块设备数据请求。在Caed层实际上完成了一个复杂的封装过程，会把request_queue->reqeust上的信息转到areq(mmc_async_req)->mmc_request上。

下面继续对mmc_start_req分析：

/***  mmc_start_req - start a non-blocking request*  @host: MMC host to start command*  @areq: async request to start*  @error: out parameter returns 0 for success, otherwise non zero**  Start a new MMC custom command request for a host.*  If there is on ongoing async request wait for completion*  of that request and start the new one and return.*  Does not wait for the new request to complete.**      Returns the completed request, NULL in case of none completed.*  Wait for the an ongoing request (previoulsy started) to complete and*  return the completed request. If there is no ongoing request, NULL*  is returned without waiting. NULL is not an error condition.*/
struct mmc_async_req *mmc_start_req(struct mmc_host *host,struct mmc_async_req *areq, int *error)
{int err = 0;int start_err = 0;struct mmc_async_req *data = host->areq;/* Prepare a new request */if (areq)mmc_pre_req(host, areq->mrq, !host->areq);if (host->areq) {err = mmc_wait_for_data_req_done(host, host->areq->mrq, areq);if (err == MMC_BLK_NEW_REQUEST) {if (error)*error = err;/** The previous request was not completed,* nothing to return*/return NULL;}/** Check BKOPS urgency for each R1 response*/if (host->card && mmc_card_mmc(host->card) &&((mmc_resp_type(host->areq->mrq->cmd) == MMC_RSP_R1) ||(mmc_resp_type(host->areq->mrq->cmd) == MMC_RSP_R1B)) &&(host->areq->mrq->cmd->resp[0] & R1_EXCEPTION_EVENT)) {/* Cancel the prepared request */if (areq)mmc_post_req(host, areq->mrq, -EINVAL);mmc_start_bkops(host->card, true);/* prepare the request again */if (areq)mmc_pre_req(host, areq->mrq, !host->areq);}}if (!err && areq)start_err = __mmc_start_data_req(host, areq->mrq);if (host->areq)mmc_post_req(host, host->areq->mrq, 0);/* Cancel a prepared request if it was not started. */if ((err || start_err) && areq)mmc_post_req(host, areq->mrq, -EINVAL);if (err)host->areq = NULL;elsehost->areq = areq;if (error)*error = err;return data;
}

mmc_wait_for_data_req_done对数据进行处理：


/** mmc_wait_for_data_req_done() - wait for request completed* @host: MMC host to prepare the command.* @mrq: MMC request to wait for** Blocks MMC context till host controller will ack end of data request* execution or new request notification arrives from the block layer.* Handles command retries.** Returns enum mmc_blk_status after checking errors.*/
static int mmc_wait_for_data_req_done(struct mmc_host *host,struct mmc_request *mrq,struct mmc_async_req *next_req)
{struct mmc_command *cmd;struct mmc_context_info *context_info = &host->context_info;int err;unsigned long flags;while (1) {wait_event_interruptible(context_info->wait,(context_info->is_done_rcv ||context_info->is_new_req));spin_lock_irqsave(&context_info->lock, flags);context_info->is_waiting_last_req = false;spin_unlock_irqrestore(&context_info->lock, flags);if (context_info->is_done_rcv) {context_info->is_done_rcv = false;context_info->is_new_req = false;cmd = mrq->cmd;if (!cmd->error || !cmd->retries ||mmc_card_removed(host->card)) {err = host->areq->err_check(host->card,host->areq);break; /* return err */} else {mmc_retune_recheck(host);pr_info("%s: req failed (CMD%u): %d, retrying...\n",mmc_hostname(host),cmd->opcode, cmd->error);cmd->retries--;cmd->error = 0;__mmc_start_request(host, mrq);continue; /* wait for done/new event again */}} else if (context_info->is_new_req) {context_info->is_new_req = false;if (!next_req)return MMC_BLK_NEW_REQUEST;}}mmc_retune_release(host);return err;
}

mmc_wait_for_data_req_done中调用__mmc_start_request(host, mrq)来执行一个请求。


static void __mmc_start_request(struct mmc_host *host, struct mmc_request *mrq)
{int err;/* Assumes host controller has been runtime resumed by mmc_claim_host */err = mmc_retune(host);if (err) {mrq->cmd->error = err;mmc_request_done(host, mrq);return;}/** For sdio rw commands we must wait for card busy otherwise some* sdio devices won't work properly.*/if (mmc_is_io_op(mrq->cmd->opcode) && host->ops->card_busy) {int tries = 500; /* Wait aprox 500ms at maximum */while (host->ops->card_busy(host) && --tries)mmc_delay(1);if (tries == 0) {mrq->cmd->error = -EBUSY;mmc_request_done(host, mrq);return;}}host->ops->request(host, mrq);
}

可以看到host->ops->request(host, mrq)，来完成request。core层其实最终都是调用mmc_host->mmc_host_ops。mmc_host_ops中放着与硬件相关的操作。内核中封装好了Card和Core两层，厂商只要按照自己的mmc控制器，编写Host层操作方法即可。

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