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

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Message-id: <57479A84.4080207@samsung.com>
Date:	Fri, 27 May 2016 09:53:24 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Shawn Lin <shawn.lin@...k-chips.com>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	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 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?

> 
> 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))


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
>