linux-kernel - Re: Issue with sequence to switch to HS400

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Date:   Tue, 30 Jul 2019 10:58:40 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Alan Cooper <alcooperx@...il.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Issue with sequence to switch to HS400

On 26/07/19 12:37 AM, Alan Cooper wrote:
> That's an even better solution and it gets my HS400 mode working.
> Will you add this change or should I?

You, if you wouldn't mind.

> 
> Thanks
> Al
> 
> On Thu, Jul 25, 2019 at 3:33 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>
>> On 23/07/19 3:34 PM, Alan Cooper wrote:
>>> On Tue, Jul 23, 2019 at 1:21 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>>>
>>>> On 23/07/19 1:31 AM, Alan Cooper wrote:
>>>>> I'm having a problem with a new SD/MMC controller and PHY in our
>>>>> latest SoC's. The issue I'm seeing is that I can't switch into HS400
>>>>> mode. This looks like something the driver is doing that doesn't meet
>>>>> the JEDEC spec. In the "HS400 timing mode selection" section of the
>>>>> JEDEC spec , in step 7 it states:
>>>>>
>>>>> 7) Set the “Timing Interface” parameter in the HS_TIMING [185] field
>>>>> of the Extended CSD register to 0x1 to switch to High Speed mode and
>>>>> then set the clock frequency to a value not greater than 52 MHz.
>>>>>
>>>>> In the function mmc_select_hs400() in mmc.c, I see that a switch
>>>>> command is done to set the eMMC device to HS mode and then
>>>>> mmc_set_timing(card->host, MMC_TIMING_MMC_HS) is used to change the
>>>>> controller to HS mode. The problem is that the "SD Host Controller
>>>>> Standard Specification" states that "UHS Mode Select" field of the
>>>>> "Host Control 2 Register" controls the mode when the "1.8V Signaling
>>>>> Enable" bit in the same register is set, so mmc_set_timing() is
>>>>> actually leaving the controller in SDR12 mode and mmc_select_hs400()
>>>>> will then set the clock to 52MHz. This causes our PHY to detect an
>>>>> illegal combination and return an error.
>>>>>
>>>>> I think the easiest fix would be to change mmc_set_timing(card->host,
>>>>> MMC_TIMING_MMC_HS) to mmc_set_timing(card->host,
>>>>> MMC_TIMING_UHS_SDR25). The other possibility would be to change
>>>>> mmc_set_timing to handle the "1.8V Signaling Enable" bit properly.
>>>>> I'll submit a patch based on the feedback I get.
>>>>
>>>> eMMC is governed by JEDEC specs not SD specs.
>>>
>>> My understanding is that JEDEC does not have a host controller spec so
>>> this driver uses the "SD Host Controller Standard Specification".
>>
>> There is no spec for using eMMC with SDHCI.
>>
>>>
>>>>
>>>> Please consider making a change in your driver instead.  For example, hook
>>>> ->set_ios() and if 1.8V is enabled and timing is set to MMC_TIMING_MMC_HS
>>>> then change it to MMC_TIMING_UHS_SDR25.
>>>
>>> That's an easy fix, but it still leaves all other drivers/systems
>>> temporarily using SDR12 at 52MHz during the switch to HS400.
>>
>> Yes, I changed my mind.  Does this work:
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>> index 59acf8e3331e..f9d241458dcd 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -1849,7 +1849,9 @@ void sdhci_set_uhs_signaling(struct sdhci_host *host, unsigned timing)
>>                 ctrl_2 |= SDHCI_CTRL_UHS_SDR104;
>>         else if (timing == MMC_TIMING_UHS_SDR12)
>>                 ctrl_2 |= SDHCI_CTRL_UHS_SDR12;
>> -       else if (timing == MMC_TIMING_UHS_SDR25)
>> +       else if (timing == MMC_TIMING_SD_HS ||
>> +                timing == MMC_TIMING_MMC_HS ||
>> +                timing == MMC_TIMING_UHS_SDR25)
>>                 ctrl_2 |= SDHCI_CTRL_UHS_SDR25;
>>         else if (timing == MMC_TIMING_UHS_SDR50)
>>                 ctrl_2 |= SDHCI_CTRL_UHS_SDR50;
>