Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964935AbaFRHjs (ORCPT ); Wed, 18 Jun 2014 03:39:48 -0400 Received: from mail-qa0-f54.google.com ([209.85.216.54]:40776 "EHLO mail-qa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964781AbaFRHjq (ORCPT ); Wed, 18 Jun 2014 03:39:46 -0400 MIME-Version: 1.0 In-Reply-To: <53A0E89F.9010006@realsil.com.cn> References: <7b58fb0b0915ea0b0838404c74ec22a3b6e5f5a8.1402037565.git.micky_ching@realsil.com.cn> <539EB43B.8070707@realsil.com.cn> <539F9412.3010209@realsil.com.cn> <53A0E89F.9010006@realsil.com.cn> Date: Wed, 18 Jun 2014 09:39:46 +0200 Message-ID: Subject: Re: [PATCH 2/2] mmc: rtsx: add support for async request From: Ulf Hansson To: micky Cc: Samuel Ortiz , Lee Jones , Chris Ball , devel@linuxdriverproject.org, "linux-kernel@vger.kernel.org" , linux-mmc , Greg Kroah-Hartman , Dan Carpenter , Roger , Wei WANG Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18 June 2014 03:17, micky wrote: > On 06/17/2014 03:45 PM, Ulf Hansson wrote: >> >> On 17 June 2014 03:04, micky wrote: >>> >>> On 06/16/2014 08:40 PM, Ulf Hansson wrote: >>>> >>>> On 16 June 2014 11:09, micky 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? mmc_request_done() ->mrq->done() ->mmc_wait_done() ->complete(&mrq->completion); > > 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. Right, I don't think there are any _problem_ by using the workqueue as you have implemented, but I am questioning if it's correct. Simply because I don't think there are any reasons to why you need a workqueue, it doesn't solve any problem for you - it just adds overhead. Kind regards Ulf Hansson -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/