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

[A.s. Dong]

> -----Original Message-----
> From: Stefan Agner [mailto:stefan@xxxxxxxx]
> Sent: Thursday, July 12, 2018 4:07 PM
> To: adrian.hunter@xxxxxxxxx; ulf.hansson@xxxxxxxxxx
> Cc: Fabio Estevam <fabio.estevam@xxxxxxx>; Bough Chen
> <haibo.chen@xxxxxxx>; A.s. Dong <aisheng.dong@xxxxxxx>; linux-
> mmc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Stefan Agner
> <stefan@xxxxxxxx>
> Subject: [PATCH v2 1/2] mmc: sdhci-esdhc-imx: disable clocks before
> changing frequency
> 
> 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.

Looks ok to me.
Acked-by: Dong Aisheng <aisheng.dong@xxxxxxx>

Regards
Dong Aisheng

> 
> Signed-off-by: Stefan Agner <stefan@xxxxxxxx>
> ---
>  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;
>  	}
> 
> --
> 2.18.0