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

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Date:	Tue, 17 Jun 2014 09:45:31 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	micky <micky_ching@...lsil.com.cn>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Chris Ball <chris@...ntf.net>, devel@...uxdriverproject.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Roger <rogerable@...ltek.com>, Wei WANG <wei_wang@...lsil.com.cn>
Subject: Re: [PATCH 2/2] mmc: rtsx: add support for async request

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

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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