linux-kernel - Re: [PATCH] mmc: sdhci-tegra: Add support to enumerate in HS400ES mode

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Message-ID: <0a8368f9-8ca2-f01b-2f9e-0c91e3b946f5@intel.com>
Date:   Thu, 2 Dec 2021 08:39:36 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Prathamesh Shete <pshete@...dia.com>, ulf.hansson@...aro.org,
        thierry.reding@...il.com, jonathanh@...dia.com,
        p.zabel@...gutronix.de, linux-mmc@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     anrao@...dia.com
Subject: Re: [PATCH] mmc: sdhci-tegra: Add support to enumerate in HS400ES
 mode

On 29/11/2021 13:10, Prathamesh Shete wrote:
> When CMD13 is sent after switching to HS400 mode, the bus
> is operating at either MMC_HIGH_26_MAX_DTR or MMC_HIGH_52_MAX_DTR.
> To meet Tegra SDHCI requirement at HS400 mode, force SDHCI
> interface clock to MMC_HS200_MAX_DTR (200 MHz) so that host
> controller CAR clock and the interface clock are rate matched.

This sounds like an issue with or without enhanced strobe?

Also it seems more like a fix than "adding support".
i.e. is this really "mmc: sdhci-tegra: Fix switch to HS400ES mode" ?

> 
> Signed-off-by: Prathamesh Shete <pshete@...dia.com>
> ---
>  drivers/mmc/host/sdhci-tegra.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
> index 387ce9cdbd7c..d800396d1112 100644
> --- a/drivers/mmc/host/sdhci-tegra.c
> +++ b/drivers/mmc/host/sdhci-tegra.c
> @@ -123,6 +123,8 @@
>  					 SDHCI_TRNS_BLK_CNT_EN | \
>  					 SDHCI_TRNS_DMA)
>  
> +static void tegra_sdhci_set_clock(struct sdhci_host *host, unsigned int clock);

Please move one of the functions so that the forward declaration is not necessary.

> +
>  struct sdhci_tegra_soc_data {
>  	const struct sdhci_pltfm_data *pdata;
>  	u64 dma_mask;
> @@ -369,6 +371,16 @@ static void tegra_sdhci_hs400_enhanced_strobe(struct mmc_host *mmc,
>  
>  	sdhci_writel(host, val, SDHCI_TEGRA_VENDOR_SYS_SW_CTRL);
>  
> +	/*
> +	 * When CMD13 is sent after switching to HS400 mode, the bus
> +	 * is operating at either MMC_HIGH_26_MAX_DTR or
> +	 * MMC_HIGH_52_MAX_DTR.
> +	 * To meet Tegra SDHCI requirement at HS400 mode, force SDHCI
> +	 * interface clock to MMC_HS200_MAX_DTR (200 MHz) so that host
> +	 * controller CAR clock and the interface clock are rate matched.
> +	 */
> +	tegra_sdhci_set_clock(host, MMC_HS200_MAX_DTR);

This being done irrespective of ios->enhanced_strobe, which doesn't seem
right based on the comment?

> +

Please remove the blank line.

>  }
>  
>  static void tegra_sdhci_reset(struct sdhci_host *host, u8 mask)
>