linux-kernel - Re: [PATCH v2 1/2] mmc: sdhci-esdhc-imx: disable clocks before changing frequency

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Message-ID: <ae108a16-80ca-0e44-d6d4-e122debc06b1@intel.com>
Date:   Thu, 12 Jul 2018 15:51:16 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Stefan Agner <stefan@...er.ch>, ulf.hansson@...aro.org
Cc:     fabio.estevam@....com, haibo.chen@....com, aisheng.dong@....com,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mmc: sdhci-esdhc-imx: disable clocks before
 changing frequency

On 12/07/18 11:07, Stefan Agner wrote:
> In the uSDHC case (e.g. i.MX 6) clocks only get disabled if frequency
> is set to 0. However, it could be that the stack asks for a frequency
> change while clocks are on. In that case the function clears the
> divider registers (by clearing ESDHC_CLOCK_MASK) while the clock is
> enabled! This causes a short period of time where the clock is
> undivided (on a i.MX 6DL a clock of 196MHz has been measured).
> 
> For older IP variants the driver disables clock by clearing some bits
> in ESDHC_SYSTEM_CONTROL.
> 
> Make sure to disable card clock before changing frequency for uSDHC
> IP variants too.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>

Acked-by: Adrian Hunter <adrian.hunter@...el.com>


> ---
>  drivers/mmc/host/sdhci-esdhc-imx.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
> index 85fd5a8b0b6d..acacd8481473 100644
> --- a/drivers/mmc/host/sdhci-esdhc-imx.c
> +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
> @@ -708,14 +708,14 @@ static inline void esdhc_pltfm_set_clock(struct sdhci_host *host,
>  	int div = 1;
>  	u32 temp, val;
>  
> +	if (esdhc_is_usdhc(imx_data)) {
> +		val = readl(host->ioaddr + ESDHC_VENDOR_SPEC);
> +		writel(val & ~ESDHC_VENDOR_SPEC_FRC_SDCLK_ON,
> +			host->ioaddr + ESDHC_VENDOR_SPEC);
> +	}
> +
>  	if (clock == 0) {
>  		host->mmc->actual_clock = 0;
> -
> -		if (esdhc_is_usdhc(imx_data)) {
> -			val = readl(host->ioaddr + ESDHC_VENDOR_SPEC);
> -			writel(val & ~ESDHC_VENDOR_SPEC_FRC_SDCLK_ON,
> -					host->ioaddr + ESDHC_VENDOR_SPEC);
> -		}
>  		return;
>  	}
>  
>