linux-kernel - Re: [RESEND PATCH v2 1/1] mmc: dw_mmc: Wait for data transfer after response errors.

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Date:	Mon, 20 Jun 2016 19:14:02 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Enric Balletbo i Serra <enric.balletbo@...labora.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	Doug Anderson <dianders@...omium.org>,
	Alim Akhtar <alim.akhtar@...il.com>
Subject: Re: [RESEND PATCH v2 1/1] mmc: dw_mmc: Wait for data transfer after
 response errors.

Hi Enric,

On 04/26/2016 05:03 PM, Enric Balletbo i Serra wrote:
> From: Doug Anderson <dianders@...omium.org>
> 
> According to the DesignWare state machine description, after we get a
> "response error" or "response CRC error" we move into data transfer
> mode. That means that we don't necessarily need to special case
> trying to deal with the failure right away. We can wait until we are
> notified that the data transfer is complete (with or without errors)
> and then we can deal with the failure.
> 
> It may sound strange to defer dealing with a command that we know will
> fail anyway, but this appears to fix a bug. During tuning (CMD19) on
> a specific card on an rk3288-based system, we found that we could get
> a "response CRC error". Sending the stop command after the "response
> CRC error" would then throw the system into a confused state causing
> all future tuning phases to report failure.

I understood this patch what purpose has.
Does it need to consider for other tuning cases?

Best Regards,
Jaehoon Chung

> 
> When in the confused state, the controller would show these (hex codes
> are interrupt status register):
>  CMD ERR: 0x00000046 (cmd=19)
>  CMD ERR: 0x0000004e (cmd=12)
>  DATA ERR: 0x00000208
>  DATA ERR: 0x0000020c
>  CMD ERR: 0x00000104 (cmd=19)
>  CMD ERR: 0x00000104 (cmd=12)
>  DATA ERR: 0x00000208
>  DATA ERR: 0x0000020c
>  ...
>  ...
> 
> It is inherently difficult to deal with the complexity of trying to
> correctly send a stop command while a data transfer is taking place
> since you need to deal with different corner cases caused by the fact
> that the data transfer could complete (with errors or without errors)
> during various places in sending the stop command (dw_mci_stop_dma,
> send_stop_abort, etc)
> 
> Instead of adding a bunch of extra complexity to deal with this, it
> seems much simpler to just use the more straightforward (and less
> error-prone) path of letting the data transfer finish. There
> shouldn't be any huge benefit to sending the stop command slightly
> earlier, anyway.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> Cc: Alim Akhtar <alim.akhtar@...il.com>
> ---
> Changelog since v1:
> - Fix the issue found by Alim with exynos letting the data transfer
>   take place only when MMC_SEND_TUNING_BLOCK is issued.
> 
>  drivers/mmc/host/dw_mmc.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 242f9a0..2ebeea8 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1761,6 +1761,33 @@ static void dw_mci_tasklet_func(unsigned long priv)
>  			}
>  
>  			if (cmd->data && err) {
> +				/*
> +				 * During UHS tuning sequence, sending the stop
> +				 * command after the response CRC error would
> +				 * throw the system into a confused state
> +				 * causing all future tuning phases to report
> +				 * failure.
> +				 *
> +				 * In such case controller will move into a data
> +				 * transfer state after a response error or
> +				 * response CRC error. Let's let that finish
> +				 * before trying to send a stop, so we'll go to
> +				 * STATE_SENDING_DATA.
> +				 *
> +				 * Although letting the data transfer take place
> +				 * will waste a bit of time (we already know
> +				 * the command was bad), it can't cause any
> +				 * errors since it's possible it would have
> +				 * taken place anyway if this tasklet got
> +				 * delayed. Allowing the transfer to take place
> +				 * avoids races and keeps things simple.
> +				 */
> +				if ((err != -ETIMEDOUT) &&
> +				    (cmd->opcode == MMC_SEND_TUNING_BLOCK)) {
> +					state = STATE_SENDING_DATA;
> +					continue;
> +				}
> +
>  				dw_mci_stop_dma(host);
>  				send_stop_abort(host, data);
>  				state = STATE_SENDING_STOP;
>