linux-kernel - Re: [PATCH v4 1/3] mmc: host: Introduce the request

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Date:   Tue, 7 Apr 2020 09:37:30 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Baolin Wang <baolin.wang7@...il.com>, ulf.hansson@...aro.org
Cc:     orsonzhai@...il.com, zhang.lyra@...il.com, arnd@...db.de,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] mmc: host: Introduce the request_atomic() for the
 host

On 3/04/20 10:05 am, Baolin Wang wrote:
> The SD host controller can process one request in the atomic context if
> the card is nonremovable, which means we can submit next request in the
> irq hard handler when using the MMC host software queue to reduce the
> latency. Thus this patch adds a new API request_atomic() for the host
> controller, as well as adding support for host software queue to submit
> a request by the new request_atomic() API.
> 
> Moreover there is an unusual case that the card is busy when trying to
> send a command, and we can not polling the card status in interrupt
> context by using request_atomic() to dispatch requests. Thus we should
> queue a work to try again in the non-atomic context in case the host
> releases the busy signal later.
> 
> Suggested-by: Adrian Hunter <adrian.hunter@...el.com>
> Signed-off-by: Baolin Wang <baolin.wang7@...il.com>


One minor point below, otherwise:

Acked-by: Adrian Hunter <adrian.hunter@...el.com>

> ---
>  drivers/mmc/host/mmc_hsq.c | 29 ++++++++++++++++++++++++++++-
>  drivers/mmc/host/mmc_hsq.h |  1 +
>  include/linux/mmc/host.h   |  3 +++
>  3 files changed, 32 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/mmc_hsq.c b/drivers/mmc/host/mmc_hsq.c
> index b90b2c9..a57f802 100644
> --- a/drivers/mmc/host/mmc_hsq.c
> +++ b/drivers/mmc/host/mmc_hsq.c
> @@ -16,11 +16,20 @@
>  #define HSQ_NUM_SLOTS	64
>  #define HSQ_INVALID_TAG	HSQ_NUM_SLOTS
>  
> +static void mmc_hsq_retry_handler(struct work_struct *work)
> +{
> +	struct mmc_hsq *hsq = container_of(work, struct mmc_hsq, retry_work);
> +	struct mmc_host *mmc = hsq->mmc;
> +
> +	mmc->ops->request(mmc, hsq->mrq);
> +}
> +
>  static void mmc_hsq_pump_requests(struct mmc_hsq *hsq)
>  {
>  	struct mmc_host *mmc = hsq->mmc;
>  	struct hsq_slot *slot;
>  	unsigned long flags;
> +	int ret = 0;
>  
>  	spin_lock_irqsave(&hsq->lock, flags);
>  
> @@ -42,7 +51,24 @@ static void mmc_hsq_pump_requests(struct mmc_hsq *hsq)
>  
>  	spin_unlock_irqrestore(&hsq->lock, flags);
>  
> -	mmc->ops->request(mmc, hsq->mrq);
> +	if (mmc->ops->request_atomic)
> +		ret = mmc->ops->request_atomic(mmc, hsq->mrq);
> +	else
> +		mmc->ops->request(mmc, hsq->mrq);
> +
> +	/*
> +	 * If returning BUSY from request_atomic(), which means the card
> +	 * may be busy now, and we should change to non-atomic context to
> +	 * try again for this unusual case, to avoid time-consuming operations
> +	 * in the atomic context.
> +	 *
> +	 * Note: we just give a warning for other error cases, since the host
> +	 * driver will handle them.
> +	 */
> +	if (ret == -EBUSY)
> +		schedule_work(&hsq->retry_work);
> +	else
> +		WARN_ON_ONCE(ret && ret != -EBUSY);

'ret != -EBUSY' is redundant because it is always true in the 'else' clause.

>  }
>  
>  static void mmc_hsq_update_next_tag(struct mmc_hsq *hsq, int remains)
> @@ -325,6 +351,7 @@ int mmc_hsq_init(struct mmc_hsq *hsq, struct mmc_host *mmc)
>  	hsq->mmc->cqe_private = hsq;
>  	mmc->cqe_ops = &mmc_hsq_ops;
>  
> +	INIT_WORK(&hsq->retry_work, mmc_hsq_retry_handler);
>  	spin_lock_init(&hsq->lock);
>  	init_waitqueue_head(&hsq->wait_queue);
>  
> diff --git a/drivers/mmc/host/mmc_hsq.h b/drivers/mmc/host/mmc_hsq.h
> index 18b9cf5..ffdd9cd 100644
> --- a/drivers/mmc/host/mmc_hsq.h
> +++ b/drivers/mmc/host/mmc_hsq.h
> @@ -12,6 +12,7 @@ struct mmc_hsq {
>  	wait_queue_head_t wait_queue;
>  	struct hsq_slot *slot;
>  	spinlock_t lock;
> +	struct work_struct retry_work;
>  
>  	int next_tag;
>  	int num_slots;
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index c318fb5..d4a50e5d 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -92,6 +92,9 @@ struct mmc_host_ops {
>  			    int err);
>  	void	(*pre_req)(struct mmc_host *host, struct mmc_request *req);
>  	void	(*request)(struct mmc_host *host, struct mmc_request *req);
> +	/* Submit one request to host in atomic context. */
> +	int	(*request_atomic)(struct mmc_host *host,
> +				  struct mmc_request *req);
>  
>  	/*
>  	 * Avoid calling the next three functions too often or in a "fast
>