linux-kernel - Re: [PATCH v2 3/4] mmc: sdhci-tegra: Issue CMD and DAT resets together

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Message-ID: <YyHHIPbXnLiPe/vn@orome>
Date:   Wed, 14 Sep 2022 14:20:48 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Prathamesh Shete <pshete@...dia.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc:     ulf.hansson@...aro.org, jonathanh@...dia.com,
        p.zabel@...gutronix.de, linux-mmc@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        anrao@...dia.com, smangipudi@...dia.com, kyarlagadda@...dia.com
Subject: Re: [PATCH v2 3/4] mmc: sdhci-tegra: Issue CMD and DAT resets
 together

On Wed, Sep 14, 2022 at 03:26:27PM +0530, Prathamesh Shete wrote:
> In case of error condition to avoid system crash
> Tegra SDMMC controller requires CMD and DAT resets
> issued together.

It might be worth specifying exactly what "system crash" means. Does
this always happen (i.e. do we have a problem right now?) or are there
specific circumstances that cause the crash.

> This is applicable to Tegra186 and later chips.
> 
> Signed-off-by: Aniruddha TVS Rao <anrao@...dia.com>
> Signed-off-by: Prathamesh Shete <pshete@...dia.com>
> ---
>  drivers/mmc/host/sdhci-tegra.c |  3 ++-
>  drivers/mmc/host/sdhci.c       | 11 ++++++++---
>  drivers/mmc/host/sdhci.h       |  2 ++
>  3 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> index b66b0cc51497..7d16dc41fe91 100644
> --- a/drivers/mmc/host/sdhci-tegra.c
> +++ b/drivers/mmc/host/sdhci-tegra.c
> @@ -1530,7 +1530,8 @@ static const struct sdhci_pltfm_data sdhci_tegra186_pdata = {
>  		  SDHCI_QUIRK_NO_HISPD_BIT |
>  		  SDHCI_QUIRK_BROKEN_ADMA_ZEROLEN_DESC |
>  		  SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN,
> -	.quirks2 = SDHCI_QUIRK2_PRESET_VALUE_BROKEN,
> +	.quirks2 = SDHCI_QUIRK2_PRESET_VALUE_BROKEN |
> +		   SDHCI_QUIRK2_ISSUE_CMD_DAT_RESET_TOGETHER,
>  	.ops  = &tegra186_sdhci_ops,
>  };
>  
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 7689ffec5ad1..289fa8ae4866 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3063,9 +3063,14 @@ static bool sdhci_request_done(struct sdhci_host *host)
>  		 * Spec says we should do both at the same time, but Ricoh
>  		 * controllers do not like that.
>  		 */

The comment above seems to indicate that the current behavior (i.e.
splitting the CMD and DATA resets) is actually the quirk, so I wonder if
this perhaps should be reversed? I suppose it could be difficult to
track down the exact controllers that need the separate resets, but this
might be worth doing. It's possible that other controllers might run
into the same issue that we are if they work strictly to the spec.

Adrian, any ideas on how much of this is just cargo-culted? Do we play
it safe and do the "double workaround" or do we want to attempt to
rectify this by adding a Ricoh-specific quirk?

Thierry

> -		sdhci_do_reset(host, SDHCI_RESET_CMD);
> -		sdhci_do_reset(host, SDHCI_RESET_DATA);
> -
> +		if (host->quirks2 &
> +			SDHCI_QUIRK2_ISSUE_CMD_DAT_RESET_TOGETHER) {
> +			sdhci_do_reset(host, SDHCI_RESET_CMD |
> +					SDHCI_RESET_DATA);
> +		} else {
> +			sdhci_do_reset(host, SDHCI_RESET_CMD);
> +			sdhci_do_reset(host, SDHCI_RESET_DATA);
> +		}
>  		host->pending_reset = false;
>  	}
>  
> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> index 95a08f09df30..8045308f7859 100644
> --- a/drivers/mmc/host/sdhci.h
> +++ b/drivers/mmc/host/sdhci.h
> @@ -480,6 +480,8 @@ struct sdhci_host {
>   * block count.
>   */
>  #define SDHCI_QUIRK2_USE_32BIT_BLK_CNT			(1<<18)
> +/* Issue CMD and DATA reset together */
> +#define SDHCI_QUIRK2_ISSUE_CMD_DAT_RESET_TOGETHER      (1<<19)
>  
>  	int irq;		/* Device IRQ */
>  	void __iomem *ioaddr;	/* Mapped address */
> -- 
> 2.17.1
> 

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