linux-kernel - Re: [RFC PATCH 2/2] mmc: dw_mmc: check card present before starting request

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Date:	Fri, 27 May 2016 10:26:58 +0800
From:	Shawn Lin <shawn.lin@...k-chips.com>
To:	Jaehoon Chung <jh80.chung@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	shawn.lin@...k-chips.com, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>,
	linux-rockchip@...ts.infradead.org
Subject: Re: [RFC PATCH 2/2] mmc: dw_mmc: check card present before starting
 request

Hi Jaehoon,

On 2016/5/27 8:53, Jaehoon Chung wrote:
> Hi Shawn,
>
> On 05/26/2016 12:08 PM, Shawn Lin wrote:
>> The main reason to add this check is to avoid unnecessary
>> mmc_request if the card is removed. Although we have already
>> check this in dw_mci_handle_cd for runtime usage of sd card and
>> dw_mci_init_slot for noremovable devices, but there is a timing
>> gap before it really calls dw_mci_get_cd as mmc_detect_change needs
>> some delay here.
>
> What's unnecessary mmc_request?

the on-going read/write/ and the corresponding sbc like cmd13, etc.


>
>>
>> Another gain here is that we could save some checkings of card status
>> after sd card been removed.
>>
>> Signed-off-by: Shawn Lin <shawn.lin@...k-chips.com>
>> ---
>>
>>  drivers/mmc/host/dw_mmc.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index cb30e91..2940d24 100644
>> --- a/drivers/mmc/host/dw_mmc.c
>> +++ b/drivers/mmc/host/dw_mmc.c
>> @@ -105,6 +105,7 @@ struct idmac_desc {
>>  static bool dw_mci_reset(struct dw_mci *host);
>>  static bool dw_mci_ctrl_reset(struct dw_mci *host, u32 reset);
>>  static int dw_mci_card_busy(struct mmc_host *mmc);
>> +static int dw_mci_get_cd(struct mmc_host *mmc);
>>
>>  #if defined(CONFIG_DEBUG_FS)
>>  static int dw_mci_req_show(struct seq_file *s, void *v)
>> @@ -1248,6 +1249,8 @@ static void dw_mci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>>
>>  	WARN_ON(slot->mrq);
>>
>> +	dw_mci_get_cd(mmc);
>> +
>
> If my understanding is right, it can be replaced
>
> if (!test_bit(DW_MMC_CARD_PRESENT, &slot->flags))
>
> to
>
> if (!dw_mci_get_cd(mmc))

yeah~ It looks better.

>
>
> Best Regards,
> Jaehoon Chung
>
>
>
>>  	/*
>>  	 * The check for card presence and queueing of the request must be
>>  	 * atomic, otherwise the card could be removed in between and the
>>
>
>
>
>


-- 
Best Regards
Shawn Lin