Re: [PATCH 2/2] mmc: rtsx: add support for async request

[micky <micky_ching@realsil.com.cn>]

On 06/17/2014 03:45 PM, Ulf Hansson wrote:
> On 17 June 2014 03:04, micky <micky_ching@realsil.com.cn> wrote:
>> On 06/16/2014 08:40 PM, Ulf Hansson wrote:
>>> On 16 June 2014 11:09, micky <micky_ching@realsil.com.cn> wrote:
>>>> On 06/16/2014 04:42 PM, Ulf Hansson wrote:
>>>>>> @@ -36,7 +37,10 @@ struct realtek_pci_sdmmc {
>>>>>>>           struct rtsx_pcr         *pcr;
>>>>>>>           struct mmc_host         *mmc;
>>>>>>>           struct mmc_request      *mrq;
>>>>>>> +       struct workqueue_struct *workq;
>>>>>>> +#define SDMMC_WORKQ_NAME       "rtsx_pci_sdmmc_workq"
>>>>>>>
>>>>>>> +       struct work_struct      work;
>>>>> I am trying to understand why you need a work/workqueue to implement
>>>>> this feature. Is that really the case?
>>>>>
>>>>> Could you elaborate on the reasons?
>>>> Hi Uffe,
>>>>
>>>> we need return as fast as possible in mmc_host_ops request(ops->request)
>>>> callback,
>>>> so the mmc core can continue handle next request.
>>>> when next request everything is ready, it will wait previous done(if not
>>>> done),
>>>> then call ops->request().
>>>>
>>>> we can't use atomic context, because we use mutex_lock() to protect
>>> ops->request should never executed in atomic context. Is that your
>>> concern?
>> Yes.
> Okay. Unless I missed your point, I don't think you need the work/workqueue.
any other method?
>
> Because, ops->request isn't ever executed in atomic context. That's
> due to the mmc core, which handles the async mechanism, are waiting
> for a completion variable in process context, before it invokes the
> ops->request() callback.
>
> That completion variable will be kicked, from your host driver, when
> you invoke mmc_request_done(), .
Sorry, I don't understand here, how kicked?

I think the flow is:
- not wait for first req
- init mrq->done
- ops->request()                         ---         A.rtsx: start queue 
work.
- continue fetch next req
- prepare next req ok,
- wait previous done.                --- B.(mmc_request_done() may be 
called at any time from A to B)
- init mrq->done
- ops->request()                         ---         C.rtsx: start queue 
next work.
...
and seems no problem.

Best Regards.
micky.
> Kind regards
> Uffe
>
>>>
>>>> resource, and we have to hold the lock during handle request.
>>>> So I use workq, we just queue a work and return in ops->request(),
>>>> The mmc core can continue without blocking at ops->request().
>>>>
>>>> Best Regards.
>>>> micky.
>>> Kind regards
>>> Uffe
>>> .
>>>
> .
>