linux-kernel - Re: [PATCH] mmc: core: Fix power sequence ordering in mmc_power

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Message-ID: <ef8580d1-989f-c9ab-abc7-034eb8cad7d0@broadcom.com>
Date:   Wed, 1 Mar 2017 10:53:46 +0100
From:   Arend Van Spriel <arend.vanspriel@...adcom.com>
To:     Romain Perier <romain.perier@...labora.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Sjoerd Simons <sjoerd.simons@...labora.co.uk>
Subject: Re: [PATCH] mmc: core: Fix power sequence ordering in mmc_power_up

On 1-3-2017 9:59, Romain Perier wrote:
> Currently, mmc_power_up calls the pre_power_on callback, enables the
> power supply of the mmc by calling mmc_set_ios() and then call
> post_power_on. WiFi chipsets like the AP6335 require a specific power
> sequence ordering before being used. You must enable the power supply
> and wait until it reaches its minimum voltage, gate the clock and wait
> at least two cycles and then assert the reset line.

Hi Romain,

You have to be more clear. What power supply, ie. vmmc or the supply for
the wifi chipset. Without knowing much of the details to me this sounds
like a new powerseq variant.

> This commit prevents regulators to be enabled in the middle of or after
> the power sequencing. We this fix, mmc_set_ios is first call, the
> underlying regulators are enabled, then pre_power_on and post_power_on
> are called, so clock and reset line are enabled in the right order,
> after the regulator.

It feels counter intuitive and maybe even wrong to change a setup
pattern like this. Can you be sure this will not cause any regressions?

Regards,
Arend

> Signed-off-by: Romain Perier <romain.perier@...labora.com>
> ---
>  drivers/mmc/core/core.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 1076b9d..36df24f 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1798,8 +1798,6 @@ void mmc_power_up(struct mmc_host *host, u32 ocr)
>  	if (host->ios.power_mode == MMC_POWER_ON)
>  		return;
>  
> -	mmc_pwrseq_pre_power_on(host);
> -
>  	host->ios.vdd = fls(ocr) - 1;
>  	host->ios.power_mode = MMC_POWER_UP;
>  	/* Set initial state and call mmc_set_ios */
> @@ -1819,13 +1817,20 @@ void mmc_power_up(struct mmc_host *host, u32 ocr)
>  	 */
>  	mmc_delay(10);
>  
> -	mmc_pwrseq_post_power_on(host);
> -
>  	host->ios.clock = host->f_init;
>  
>  	host->ios.power_mode = MMC_POWER_ON;
>  	mmc_set_ios(host);
>  
> +	mmc_pwrseq_pre_power_on(host);
> +
> +	/*
> +	 * This delay should be sufficient to wait at least two cycles of clock
> +	 * gated by pre_power_on
> +	 */
> +	mmc_delay(1);
> +	mmc_pwrseq_post_power_on(host);
> +
>  	/*
>  	 * This delay must be at least 74 clock sizes, or 1 ms, or the
>  	 * time required to reach a stable voltage.
>