linux-kernel - Re: [PATCH v2 11/40] mmc: sdhci: Add a quirk to skip clearing the transfer mode register on tuning

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Date:   Mon, 27 Aug 2018 14:01:52 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Aapo Vienamo <avienamo@...dia.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Stefan Agner <stefan@...er.ch>
Cc:     devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH v2 11/40] mmc: sdhci: Add a quirk to skip clearing the
 transfer mode register on tuning

On 10/08/18 21:08, Aapo Vienamo wrote:
> Add SDHCI_QUIRK2_TUNE_SKIP_XFERRMODE_REG_PROG to skip programming the
> SDHCI_TRANSFER_MODE in sdhci_set_transfer_mode() if tuning command is
> being sent.
> 
> On Tegra210 and Tegra186 the tuning sequence hangs if the SDHCI
> transfer mode register is touched.
> 
> Signed-off-by: Aapo Vienamo <avienamo@...dia.com>
> ---
>  drivers/mmc/host/sdhci.c | 6 ++++++
>  drivers/mmc/host/sdhci.h | 2 ++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index a7b5602..04dc443 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1028,6 +1028,12 @@ static void sdhci_set_transfer_mode(struct sdhci_host *host,
>  
>  	if (data == NULL) {
>  		if (host->quirks2 &
> +			SDHCI_QUIRK2_TUNE_SKIP_XFERMODE_REG_PROG &&
> +				(cmd->opcode == MMC_SEND_TUNING_BLOCK ||
> +				 cmd->opcode == MMC_SEND_TUNING_BLOCK_HS200)) {
> +			return;
> +		}

Rather than introduce a quirk, can't we just dodge the unnecessary write e.g.

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 1b3fbd9bd5c5..68af6a67e397 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1033,10 +1033,19 @@ static void sdhci_set_transfer_mode(struct sdhci_host *host,
 			if (cmd->opcode != MMC_SEND_TUNING_BLOCK_HS200)
 				sdhci_writew(host, 0x0, SDHCI_TRANSFER_MODE);
 		} else {
-		/* clear Auto CMD settings for no data CMDs */
+			u16 orig;
+
+			/* clear Auto CMD settings for no data CMDs */
 			mode = sdhci_readw(host, SDHCI_TRANSFER_MODE);
-			sdhci_writew(host, mode & ~(SDHCI_TRNS_AUTO_CMD12 |
-				SDHCI_TRNS_AUTO_CMD23), SDHCI_TRANSFER_MODE);
+			orig = mode;
+			mode &= ~(SDHCI_TRNS_AUTO_CMD12 | SDHCI_TRNS_AUTO_CMD23);
+			/*
+			 * Do not write transfer mode unnecessarily because it
+			 * can upset some host controllers (e.g. sdhci-tregra)
+			 * during tuning.
+			 */
+			if (mode != orig)
+				sdhci_writew(host, new_mode, SDHCI_TRANSFER_MODE);
 		}
 		return;
 	}


Alternatively 

> +		if (host->quirks2 &
>  			SDHCI_QUIRK2_CLEAR_TRANSFERMODE_REG_BEFORE_CMD) {
>  			sdhci_writew(host, 0x0, SDHCI_TRANSFER_MODE);
>  		} else {
> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
> index 23966f8..0a99008 100644
> --- a/drivers/mmc/host/sdhci.h
> +++ b/drivers/mmc/host/sdhci.h
> @@ -450,6 +450,8 @@ struct sdhci_host {
>   * obtainable timeout.
>   */
>  #define SDHCI_QUIRK2_DISABLE_HW_TIMEOUT			(1<<17)
> +/* Don't clear the SDHCI_TRANSFER_MODE register on tuning commands */
> +#define SDHCI_QUIRK2_TUNE_SKIP_XFERMODE_REG_PROG	(1<<18)
>  
>  	int irq;		/* Device IRQ */
>  	void __iomem *ioaddr;	/* Mapped address */
>