linux-kernel - Re: [PATCH 2/2] mmc: sdhci: Defer probe if regulator

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Date:	Tue, 23 Oct 2012 10:23:58 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Pavan Kunapuli <pkunapuli@...dia.com>
CC:	linux@....linux.org.uk, cjb@...top.org,
	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH 2/2] mmc: sdhci: Defer probe if regulator_get fails

On 10/23/2012 01:18 AM, Pavan Kunapuli wrote:
> vmmc and vqmmc regulators control the voltage to
> the host and device. Defer the probe if either of
> them is not registered.
> 
> Signed-off-by: Pavan Kunapuli <pkunapuli@...dia.com>
> ---
>  drivers/mmc/host/sdhci.c |   25 ++++++++++++++++++++++---
>  1 files changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
> index 7922adb..925c403 100644
> --- a/drivers/mmc/host/sdhci.c
> +++ b/drivers/mmc/host/sdhci.c
> @@ -2844,11 +2844,17 @@ int sdhci_add_host(struct sdhci_host *host)
>  	    !(host->mmc->caps & MMC_CAP_NONREMOVABLE))
>  		mmc->caps |= MMC_CAP_NEEDS_POLL;
>  
> -	/* If vqmmc regulator and no 1.8V signalling, then there's no UHS */
> +	/*
> +	 * If vqmmc regulator and no 1.8V signalling, then there's no UHS.
> +	 * vqmmc regulator should be present. If it's not present,
> +	 * assume the regulator driver registration is not yet done and
> +	 * defer the probe.
> +	 */
>  	host->vqmmc = regulator_get(mmc_dev(mmc), "vqmmc");
>  	if (IS_ERR(host->vqmmc)) {
> -		pr_info("%s: no vqmmc regulator found\n", mmc_hostname(mmc));
> +		pr_err("%s: no vqmmc regulator found\n", mmc_hostname(mmc));
>  		host->vqmmc = NULL;
> +		return -EPROBE_DEFER;
>  	}

Right now, the regulator is optional, and any failure to acquire the
regulator is just ignored.

Instead, I think the behaviour we want is:

Attempt to get regulator.
1) If no error -> OK
2) If deferred probe error -> return -EPROBE_DEFER
3) If any other error -> ignore it

Assuming that regulator_get() can explicitly detect and return the
difference between cases (1) and (2) above. If it can't, it seems like
it should be able to.
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