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

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Date:   Tue, 7 Apr 2020 13:14:17 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Baolin Wang <baolin.wang7@...il.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] mmc: host: Introduce the request_atomic() for the
 host

On 7/04/20 10:21 am, Baolin Wang wrote:
> On Tue, Apr 7, 2020 at 2:38 PM Adrian Hunter <adrian.hunter@...el.com> 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@...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.
> 
> 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.
> 

I'd like to handle the inhibit wait differently.  I will make some patches
for that and send them out.