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

From: Kishon Vijay Abraham I
Date: Thu Apr 26 2018 - 06:08:51 EST

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@xxxxxx>
>> Acked-by: Tony Lindgren <tony@xxxxxxxxxxx>
>> ---
>> 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 |
>> + 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.