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

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Message-ID: <CAOGqxeUwXEYr493N-=jNBxHwDgWyAiKfER=mJbnEMMAL2EQF7g@mail.gmail.com>
Date:   Mon, 5 Aug 2019 15:43:52 -0400
From:   Alan Cooper <alcooperx@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.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

No problem.

Thanks
Al

On Tue, Jul 30, 2019 at 4:00 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> 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;
> >
>