linux-kernel - Re: [PATCH V2 1/7] mmc: sdhci: add sd host v4 mode

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Date:   Wed, 4 Jul 2018 11:02:31 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Chunyan Zhang <zhang.chunyan@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Orson Zhai <orsonzhai@...il.com>,
        Baolin Wang <baolin.wang@...aro.org>,
        Billows Wu <billows.wu@...eadtrum.com>
Subject: Re: [PATCH V2 1/7] mmc: sdhci: add sd host v4 mode

On 21 June 2018 at 21:15, Adrian Hunter <adrian.hunter@...el.com> wrote:
> On 21/06/18 14:14, Chunyan Zhang wrote:
>> On 21 June 2018 at 18:49, Adrian Hunter <adrian.hunter@...el.com> wrote:
>>> On 15/06/18 05:04, Chunyan Zhang wrote:
>>>> For SD host controller version 4.00 or later ones, there're two
>>>> modes of implementation - Version 3.00 compatible mode or
>>>> Version 4 mode.  This patch introduces a flag to record this.
>>>>
>>>> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
>>>> ---
>>>>  drivers/mmc/host/sdhci.c | 6 ++++++
>>>>  drivers/mmc/host/sdhci.h | 6 ++++++
>>>>  2 files changed, 12 insertions(+)
>>>>
>>>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
>>>> index 2ededa7f..cf5695f 100644
>>>> --- a/drivers/mmc/host/sdhci.c
>>>> +++ b/drivers/mmc/host/sdhci.c
>>>> @@ -3302,6 +3302,12 @@ void __sdhci_read_caps(struct sdhci_host *host, u16 *ver, u32 *caps, u32 *caps1)
>>>>       v = ver ? *ver : sdhci_readw(host, SDHCI_HOST_VERSION);
>>>>       host->version = (v & SDHCI_SPEC_VER_MASK) >> SDHCI_SPEC_VER_SHIFT;
>>>>
>>>> +     if (host->version >= SDHCI_SPEC_400) {
>>>> +             if (sdhci_readw(host, SDHCI_HOST_CONTROL2) &
>>>> +                     SDHCI_CTRL_V4_MODE)
>>>> +                     host->v4_mode = true;
>>>> +     }
>>>
>>> At this point the host controller has just been reset which would mean it
>>> must be in version 3 compatibility mode, which would mean this code doesn't
>>> do anything.
>>
>> Why is it version 3 mode at this point?
>
> According to the specification, reset clears RW fields to zero.
>
>>
>> I've tested this code on the sd host controller which was introduced
>> in 6/7 in this patch-set, the result showed that it was v4_mode.
>> Moreover without this patch, the Spreadtrum's sdhci driver in patch
>> 6/7 couldn't work.
>>
>> Am I missing something here?
>
> It seems the Spreadtrum controller doesn't clear the "Host Version 4 Enable"
> bit upon software reset for all.
>
> Also this seems the wrong way around.  The driver should decide whether or
> not to use V4 mode and then the "Host Version 4 Enable" bit should be set
> accordingly.
>
> V4 has been around so long that we can't just enable all supporting hardware
> without risking the possibility it will break some platform.  So I suggest

Ok, understand.

> adding a function sdhci_enable_v4_mode() which is called during probe.

Ok, will do, that is more a safe way.

>
>>
>> Best,
>> Chunyan
>>
>>>
>>>> +
>>>>       if (host->quirks & SDHCI_QUIRK_MISSING_CAPS)
>>>>               return;
>>>>
>>>> diff --git a/drivers/mmc/host/sdhci.h b/drivers/mmc/host/sdhci.h
>>>> index c95b0a4..128b0ba 100644
>>>> --- a/drivers/mmc/host/sdhci.h
>>>> +++ b/drivers/mmc/host/sdhci.h
>>>> @@ -184,6 +184,7 @@
>>>>  #define   SDHCI_CTRL_DRV_TYPE_D              0x0030
>>>>  #define  SDHCI_CTRL_EXEC_TUNING              0x0040
>>>>  #define  SDHCI_CTRL_TUNED_CLK                0x0080
>>>> +#define  SDHCI_CTRL_V4_MODE          0x1000
>>>>  #define  SDHCI_CTRL_PRESET_VAL_ENABLE        0x8000
>>>>
>>>>  #define SDHCI_CAPABILITIES   0x40
>>>> @@ -270,6 +271,8 @@
>>>>  #define   SDHCI_SPEC_100     0
>>>>  #define   SDHCI_SPEC_200     1
>>>>  #define   SDHCI_SPEC_300     2
>>>> +#define   SDHCI_SPEC_400     3
>>>> +#define   SDHCI_SPEC_410     4
>>>>
>>>>  /*
>>>>   * End of controller registers.
>>>> @@ -551,6 +554,9 @@ struct sdhci_host {
>>>>       u32                     sdma_boundary;
>>>>
>>>>       unsigned long private[0] ____cacheline_aligned;
>>>> +
>>>> +     /* Host Version 4 Enable */
>>>> +     bool                    v4_mode;
>>>>  };
>>>>
>>>>  struct sdhci_ops {
>>>>
>>>
>>
>