Re: [PATCH v4 1/3] mmc: host: Introduce the request_atomic() for the host

[Baolin Wang]

On Tue, Apr 7, 2020 at 2:38 PM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx>
> > Signed-off-by: Baolin Wang <baolin.wang7@xxxxxxxxx>
>
>
> One minor point below, otherwise:
>
> Acked-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
>
> > ---
> >  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.

Ah, Yes, thanks for pointing this out and I will fix it ine next version.

By the way, could you help to review patch 2 and 3 in this patch set? Thanks.

> >  }
> >
> >  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
> >
>


-- 
Baolin Wang