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SubjectRe: [PATCH v4 1/3] mmc: host: Introduce the request_atomic() for the host
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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@intel.com>
> Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>


One minor point below, otherwise:

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

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