Re: [PATCH v3] mmc: sdhci: wait 5ms after set 1.8V signal enable

[Adrian Hunter <adrian.hunter@intel.com>]

On 15/12/17 21:28, Zhoujie Wu wrote:
> According to SD spec 3.00 3.6.1 signal voltage switch
> procedure step 6~8,
> (6) Set 1.8V Signal Enable in the Host Control 2 register.
> (7) Wait 5ms. 1.8V voltage regulator shall be stable within this period.
> (8) If 1.8V Signal Enable is cleared by Host Controller, go to step (12).
> 
> Host should wait 5ms after set 1.8V signal enable bit in
> Host Control 2 register and check if 1.8V is stable or not.
> 
> But current code checks if this bit is cleared by controller
> right after set it. On some platforms found the bit is not
> cleared right away and host reports "1.8V regulator output
> did not became stable" and 5ms delay can help.

The check is for the bit set not cleared.

> 
> Follow the spec and add 5ms delay to make sure the 1.8V Signal Enable
> bit is cleared.
> 
> Signed-off-by: Zhoujie Wu <zjwu@marvell.com>
> ---
>  drivers/mmc/host/sdhci.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index e9290a3..fe5f208 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -1933,6 +1933,9 @@ int sdhci_start_signal_voltage_switch(struct mmc_host *mmc,
>  		if (host->ops->voltage_switch)
>  			host->ops->voltage_switch(host);
>  
> +		/* Wait for 5ms */
> +		usleep_range(5000, 5500);

We have managed without this delay for a while and I am reluctant to add
delays that might anyway be specific to the controller.  What do you think
about implementing ->voltage_switch() and putting the delay there?

> +
>  		/* 1.8V regulator output should be stable within 5 ms */
>  		ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2);
>  		if (ctrl & SDHCI_CTRL_VDD_180)
>