linux-kernel - Re: [PATCH v4 05/12] mmc: sdhci: Disable HS200/HS400 mode if controller can't support 1.8v

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Date:   Thu, 26 Apr 2018 15:38:35 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH v4 05/12] mmc: sdhci: Disable HS200/HS400 mode if
 controller can't support 1.8v

Hi Adrian,

On Thursday 26 April 2018 02:25 PM, Adrian Hunter wrote:
> On 25/04/18 15:09, Kishon Vijay Abraham I wrote:
>> Though MMC controller can indicate HS200/HS400 mode capability (by
>> using "mmc-hs200-1_8v"/"mmc-hs400-1_8v" dt property), if the IO lines
>> in the board is connected to 3.3v supply, HS200/HS400 mode cannot be
>> supported. Such boards have "no-1-8-v" property in their dts file.
>> Disable HS200/HS400 mode for boards which have "no-1-8-v" set.
>>
>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>> Acked-by: Tony Lindgren <tony@...mide.com>
>> ---
>>  drivers/mmc/host/sdhci.c | 1 +
>>  include/linux/mmc/host.h | 1 +
>>  2 files changed, 2 insertions(+)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index 2ededa7f43df..b5f047b5f3ae 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -3672,6 +3672,7 @@ int sdhci_setup_host(struct sdhci_host *host)
>>  	if (host->quirks2 & SDHCI_QUIRK2_NO_1_8_V) {
>>  		host->caps1 &= ~(SDHCI_SUPPORT_SDR104 | SDHCI_SUPPORT_SDR50 |
>>  				 SDHCI_SUPPORT_DDR50);
>> +		mmc->caps2 &= ~MMC_CAP2_HSX00_1_8V;
> 
> Seems weird for sdhci to clear flags it never set.  Also couldn't we
> reasonably expect dt properties to be consistent?  Is this really about
> setting SDHCI_QUIRK2_NO_1_8_V in your driver and expecting it to override
> other dt properties?  Although that still begs the question why anyone would
> set dt properties that the hardware doesn't support?  I guess you should
> also clear MMC_CAP2_HS400_ES.

The SoC might support a specific mode like HS200. So the SoC specific dtsi file
might have dt properties for HS200 mode set. But the board which uses the SoC
might be modeled in a way a particular mode cannot be used (like IO lines not
connected to 1.8v). One option is to use /delete-property/ in the board dts
file. But since "no-1-8-v" property already indicates HS200 mode cannot be
supported, having a /delete-property/ might be redundant.

I can reset caps2 in sdhci-omap after invoking mmc_of_parse if you feel that
makes more sense.

Thanks
Kishon