linux-kernel - Re: [PATCH] mmc: sdhci: Fix incorrect switch to HS mode

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Message-ID: <7e495749-1539-9164-d801-305a918318d6@ti.com>
Date:   Thu, 28 Nov 2019 13:51:14 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Alan Cooper <alcooperx@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH] mmc: sdhci: Fix incorrect switch to HS mode

Hi,

On 19/09/19 5:27 PM, Alan Cooper wrote:
> This does correct the sequence of switching to HS400 but it might be
> safest to just add this to the latest until it gets a little testing
> to make sure it doesn't expose some bug in existing controllers.
> 
> Thanks
> Al
> 
> On Tue, Sep 3, 2019 at 10:52 AM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>
>> On Tue, 3 Sep 2019 at 13:51, Al Cooper <alcooperx@...il.com> wrote:
>>>
>>> When switching from any MMC speed mode that requires 1.8v
>>> (HS200, HS400 and HS400ES) to High Speed (HS) mode, the system
>>> ends up configured for SDR12 with a 50MHz clock which is an illegal
>>> mode.
>>>
>>> This happens because the SDHCI_CTRL_VDD_180 bit in the
>>> SDHCI_HOST_CONTROL2 register is left set and when this bit is
>>> set, the speed mode is controlled by the SDHCI_CTRL_UHS field
>>> in the SDHCI_HOST_CONTROL2 register. The SDHCI_CTRL_UHS field
>>> will end up being set to 0 (SDR12) by sdhci_set_uhs_signaling()
>>> because there is no UHS mode being set.
>>>
>>> The fix is to change sdhci_set_uhs_signaling() to set the
>>> SDHCI_CTRL_UHS field to SDR25 (which is the same as HS) for
>>> any switch to HS mode.

This change has broken High speed mode in SD card for me in AM65x-evm. I
guess this change only needs to be done for eMMC. SDR25 is decidedly not
the same as high speed for SD card.

Thanks,
Faiz