linux-kernel - Re: [PATCH v4 3/3] mmc: dw_mmc: Don't start command while data busy

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Date:	Thu, 19 Feb 2015 16:21:31 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Addy Ke <addy.ke@...k-chips.com>
Cc:	Jaehoon Chung <jh80.chung@...sung.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Alim Akhtar <alim.akhtar@...il.com>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Heiko Stübner <heiko@...ech.de>,
	Eddie Cai <cf@...k-chips.com>, lintao <lintao@...k-chips.com>,
	Tao Huang <huangtao@...k-chips.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Subject: Re: [PATCH v4 3/3] mmc: dw_mmc: Don't start command while data busy

Addy,

On Fri, Feb 13, 2015 at 10:17 PM, Addy Ke <addy.ke@...k-chips.com> wrote:
> We should wait until unbusy before the next request.
> But this does't need if the command is CMD13, which can access
> SD Status register regardless of data busy.
>
> Signed-off-by: Addy Ke <addy.ke@...k-chips.com>
> ---
> Changes in v4:
> - CMD13 doesn't need wait until unbusy.
>
>  drivers/mmc/host/dw_mmc.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index ac21863..692d97a 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1076,6 +1076,10 @@ static void dw_mci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>
>         WARN_ON(slot->mrq);
>
> +       /* Wait until unbusy if the command isn't CMD13 */
> +       if (mrq->cmd->opcode != MMC_SEND_STATUS)
> +               dw_mci_wait_busy(slot);
> +

I think you need to be more general.  You really should be checking
"cmd_flags & SDMMC_CMD_PRV_DAT_WAIT".  That leverages dw_mmc's
knowledge about whether it needs to wait.  Right now you'll be waiting
for CMD52 (SDIO) which I don't think is a good idea.

It also seems like this would be better in dw_mci_start_command() so
that we have the least chance of hitting the case.  The downside is
that you can't sleep there, though...  Hrm.

I updated a version of my take on this at
<https://chromium-review.googlesource.com/#/c/244850/>.  I'll put a
timeout on it soon-ish.  Any extra testing that folks can do would be
appreciated...

-Doug
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