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

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Message-ID: <578F76DF.1000500@intel.com>
Date:	Wed, 20 Jul 2016 16:04:31 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Jon Hunter <jonathanh@...dia.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>
Cc:	linux-mmc@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 1/2] mmc: sdhci: Request regulators before reading
 capabilities

On 20/07/16 16:02, Adrian Hunter wrote:
> On 12/07/16 16:53, Jon Hunter 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
> 
> Try not to confuse High Speed mode with UHS modes.
> 
> presense -> presence
> 
>> regulators before reading the capabilites of the host controller. This
> 
> capabilites -> capabilities
> 
>> 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>
>> ---
>>
>> 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().
> 
> And we can still do that later if we need to.
> 
>>
>>  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.

Also you could spread this comment out to 80 columns.

>> +	 */
>> +	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;
> 
> All goto's before this now need to goto unreg.
> 
>> -
>>  	/* 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);
>>
> 
>