Date:   Wed, 24 Jul 2019 15:55:04 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Baolin Wang <baolin.wang@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Chunyan Zhang <zhang.lyra@...il.com>,
        Orson Zhai <orsonzhai@...il.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mmc: host: sdhci-sprd: Fix the incorrect soft reset
 operation when runtime resuming

On 24/07/19 5:21 AM, Baolin Wang wrote:
> On Tue, 23 Jul 2019 at 20:39, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>
>> On Tue, 23 Jul 2019 at 05:05, Baolin Wang <baolin.wang@...aro.org> wrote:
>>>
>>> Hi Ulf,
>>>
>>> On Mon, 22 Jul 2019 at 19:54, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>>>
>>>> On Wed, 17 Jul 2019 at 04:29, Baolin Wang <baolin.wang@...aro.org> wrote:
>>>>>
>>>>> In sdhci_runtime_resume_host() function, we will always do software reset
>>>>> for all, which will cause Spreadtrum host controller work abnormally after
>>>>> resuming.
>>>>
>>>> What does "software reset for all" means?
>>>
>>> The SD host controller specification defines 3 types software reset:
>>> software reset for data line, software reset for command line and
>>> software reset for all.
>>> Software reset for all means this reset affects the entire Host
>>> controller except for the card detection circuit.
>>
>> Thanks for clarifying, please update the changelog accordingly.
> 
> Sure, sorry for confusing.
> 
>>
>>>
>>>>
>>>>>
>>>>> Thus for Spreadtrum platform that will not power down the SD/eMMC card during
>>>>> runtime suspend, we should not do software reset for all.
>>>>
>>>> Normally, sdhci hosts that enters runtime suspend doesn't power off
>>>> the card (there are some exceptions like PCI variants).
>>>
>>> Yes, same as our controller.
>>>
>>>>
>>>> So, what's so special here and how does the reset come into play? I
>>>> don't see sdhci doing a reset in sdhci_runtime_suspend|resume_host()
>>>> and nor doesn the callback from the sdhci-sprd.c variant doing it.
>>>
>>> In sdhci_runtime_resume_host(), it will issue sdhci_init(host, 0) to
>>> issue software reset for all.
>>
>> Aha, I didn't read the code carefully enough. Apologize for the noise.
> 
> No worries :)
> 
>>>
>>>>
>>>>> To fix this
>>>>> issue, adding a specific reset operation that adds one condition to validate
>>>>> the power mode to decide if we can do software reset for all or just reset
>>>>> command and data lines.
>>>>>
>>>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>>>> ---
>>>>> Changess from v3:
>>>>>  - Use ios.power_mode to validate if the card is power down or not.
>>>>>
>>>>> Changes from v2:
>>>>>  - Simplify the sdhci_sprd_reset() by issuing sdhci_reset().
>>>>>
>>>>> Changes from v1:
>>>>>  - Add a specific reset operation instead of changing the core to avoid
>>>>>  affecting other hardware.
>>>>> ---
>>>>>  drivers/mmc/host/sdhci-sprd.c |   19 ++++++++++++++++++-
>>>>>  1 file changed, 18 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/mmc/host/sdhci-sprd.c b/drivers/mmc/host/sdhci-sprd.c
>>>>> index 603a5d9..94f9726 100644
>>>>> --- a/drivers/mmc/host/sdhci-sprd.c
>>>>> +++ b/drivers/mmc/host/sdhci-sprd.c
>>>>> @@ -373,6 +373,23 @@ static unsigned int sdhci_sprd_get_max_timeout_count(struct sdhci_host *host)
>>>>>         return 1 << 31;
>>>>>  }
>>>>>
>>>>> +static void sdhci_sprd_reset(struct sdhci_host *host, u8 mask)
>>>>> +{
>>>>> +       struct mmc_host *mmc = host->mmc;
>>>>> +
>>>>> +       /*
>>>>> +        * When try to reset controller after runtime suspend, we should not
>>>>> +        * reset for all if the SD/eMMC card is not power down, just reset
>>>>> +        * command and data lines instead. Otherwise will meet some strange
>>>>> +        * behaviors for Spreadtrum host controller.
>>>>> +        */
>>>>> +       if (host->runtime_suspended && (mask & SDHCI_RESET_ALL) &&
>>>>> +           mmc->ios.power_mode == MMC_POWER_ON)
>>>>> +               mask = SDHCI_RESET_CMD | SDHCI_RESET_DATA;
>>>>
>>>> Can sdhci_sprd_reset() be called when the host is runtime suspended?
>>>
>>> When host tries to runtime resume in sdhci_runtime_resume_host(), it
>>> will call reset operation to do software reset.
>>
>> Right, I see that now, thanks for clarifying.
>>
>> However, there are still some weird things going on in
>> sdhci_runtime_resume_host(). Like why is host->ops->enable_dma()
>> called first, directly from sdhci_runtime_resume_host(), then again in
>> sdhci_do_reset(), after host->ops->reset() has been called. Looks like
>> the first call to ->enable_dma() doesn't make sense?
> 
> I am mot sure, since our host did not supply enable_dma() operation.
> This logic was used by some other hardware and worked well, I am not
> sure if it can reveal some issues if we change the logic here.
> 
> Adrian, could you help to explain why we put enable_dma() in front of
> software reset?

No reason I can see.  But if you add a parameter to avoid a full reset, then
the ->enable_dma will be needed in that case.

> 
>>
>>>
>>>> That sounds like a bug to me, no?
>>>
>>> Since our controller will meet some strange behaviors if we do
>>> software reset for all in sdhci_runtime_resume_host(), and try to
>>> avoid changing the core logic of sdhci_runtime_resume_host() used by
>>> other hardware controllers, thus I introduced a specific reset ops and
>>> added some condition to make sure we just do software reset command
>>> and data lines from runtime suspend state.
>>
>> I understand, but perhaps it would become more clear if
>> sdhci_runtime_resume_host() is re-factored a bit. Maybe the caller can
>> give it some new parameter to let it decide if a SDHCI_RESET_ALL shall
>> be done or not.
> 
> Yes, sounds reasonable, but need change other host drivers which
> issued the sdhci_runtime_resume_host().
> 
> Adrian, if you also agree with Ulf's suggestion, then I will post new
> patches to add a parameter to decide the reset mode. Thanks.

Sounds fine.

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