linux-kernel - Re: [PATCH V2 1/2] mmc: sdhci: Request regulators before reading capabilities

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Date:	Sat, 23 Jul 2016 11:37:58 +0200
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Adrian Hunter <adrian.hunter@...el.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] mmc: sdhci: Request regulators before reading capabilities

On 12 July 2016 at 15:53, Jon Hunter <jonathanh@...dia.com> wrote:
> The capabilities of the SDHCI host controller are read early during the
> SDHCI host initialisation in sdhci_setup_host() and before any
> regulators for the host have been requested. This means that if the host
> supports some high-speed modes (according to its capabilities register),
> but the board cannot because the appropriate voltage regulator is not
> available, then the host cannot easily override the capabilities that
> are supported.
>
> To allow a SDHCI host controller to determine if it can support high
> speed modes via the presense of the MMC regulators, request the
> regulators before reading the capabilites of the host controller. This
> will allow the SDHCI host to use the 'reset' callback to take the
> appropriate action (set flags, configure registers, etc) before the
> capabilities register(s) are read.
>
> Please note that some SDHCI hosts, such as the Tegra SDHCI host, has
> the ability to mask bits in the capabilities register to prevent
> certain capabilities from being advertised.
>
> Signed-off-by: Jon Hunter <jonathanh@...dia.com>

Thanks, applied for next! I changed the minor things pointed out by Adrian.

Kind regards
Uffe


> ---
>
> Although this is described as a "V2" this patch has been added since
> the original patch was posted.
>
> If the below is deemed not appropriate, then another solution I was
> thinking of is to allow the SDHCI host to call 'mmc_regulator_get_supply'
> before calling sdhci_setup_host() and then in sdhci_setup_host() check
> if any regulators are already present before calling
> mmc_regulator_get_supply().
>
>  drivers/mmc/host/sdhci.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 2ee8bfa77116..628c4b3558c0 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -3021,6 +3021,17 @@ int sdhci_setup_host(struct sdhci_host *host)
>
>         mmc = host->mmc;
>
> +       /*
> +        * If there are external regulators, get them. Note
> +        * this must be done early before resetting the host
> +        * and reading the capabilities so that the host can
> +        * take the appropriate action if regulators are not
> +        * available.
> +        */
> +       ret = mmc_regulator_get_supply(mmc);
> +       if (ret == -EPROBE_DEFER)
> +               return ret;
> +
>         sdhci_read_caps(host);
>
>         override_timeout_clk = host->timeout_clk;
> @@ -3253,11 +3264,6 @@ int sdhci_setup_host(struct sdhci_host *host)
>             mmc_gpio_get_cd(host->mmc) < 0)
>                 mmc->caps |= MMC_CAP_NEEDS_POLL;
>
> -       /* If there are external regulators, get them */
> -       ret = mmc_regulator_get_supply(mmc);
> -       if (ret == -EPROBE_DEFER)
> -               goto undma;
> -
>         /* If vqmmc regulator and no 1.8V signalling, then there's no UHS */
>         if (!IS_ERR(mmc->supply.vqmmc)) {
>                 ret = regulator_enable(mmc->supply.vqmmc);
> --
> 2.1.4
>