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

[Ulf Hansson]

On 17 June 2014 03:04, micky <micky_ching@xxxxxxxxxxxxxx> wrote:
> On 06/16/2014 08:40 PM, Ulf Hansson wrote:
>>
>> On 16 June 2014 11:09, micky <micky_ching@xxxxxxxxxxxxxx> 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.

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(), .

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
>> .
>>
>
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