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

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Date:	Fri, 27 May 2016 12:46:14 +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: [PATCH 2/2] mmc: dw_mmc: check card present before starting request

Hi Shawn,

On 05/27/2016 12:02 PM, Shawn Lin wrote:
> The main reason to add this check is to avoid unnecessary
> mmc_request like the on-going cmd and the corresponding sbc
> if the card is removed. Although we have already checked 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.
> 
> 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, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index cb30e91..8eb7898 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)
> @@ -1255,7 +1256,7 @@ static void dw_mci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>  	 */
>  	spin_lock_bh(&host->lock);
>  
> -	if (!test_bit(DW_MMC_CARD_PRESENT, &slot->flags)) {
> +	if (!dw_mci_get_cd(mmc)) {
>  		spin_unlock_bh(&host->lock);
>  		mrq->cmd->error = -ENOMEDIUM;
>  		mmc_request_done(mmc, mrq);

I think spin_lock/unlock_bh() should be removed at here.
Instead, Can it locate before calling dw_mci_queue_request()?

Anyway, it looks good to me.

Best Regards,
Jaehoon Chung

>