Re: [PATCH 7/10] mmc: sdhci-xenon: Add support to PHYs of Marvell Xenon SDHC

[Ulf Hansson]

On 29 November 2016 at 03:53, Ziji Hu <huziji@xxxxxxxxxxx> wrote:
> Hi Ulf,
>
> On 2016/11/28 23:16, Ulf Hansson wrote:
>> On 28 November 2016 at 12:38, Ziji Hu <huziji@xxxxxxxxxxx> wrote:
>>> Hi Ulf,
>>>
>>> On 2016/11/28 19:13, Ulf Hansson wrote:
>>>>>
>>>>>     As you suggest, I replace mmc_wait_for_cmd() with mmc_send_tuning(), to
>>>>>     send commands for testing current sampling point set in our host PHY.
>>>>>
>>>>>     According to my test result, it shows that mmc_send_tuning() can only support
>>>>>     tuning command (CMD21/CMD19).
>>>>>     As a result, we cannot use mmc_send_tuning() when card is in the speed modes
>>>>>     which doesn't support tuning, such as eMMC HS SDR, eMMC HS DRR and
>>>>>     SD SDR 12/SDR25/DDR50. Card will not response to tuning commands in those
>>>>>     speed modes.
>>>>>
>>>>>     Could you please provide suggestions for the speed mode in which tuning is
>>>>>     not available?
>>>>>
>>>>
>>>> Normally the mmc host driver shouldn't have to care about what the
>>>> card supports, as that is the responsibility of the mmc core to
>>>> manage.
>>>>
>>>> The host should only need to implement the ->execute_tuning() ops,
>>>> which gets called when the card supports tuning (CMD19/21). Does it
>>>> make sense?
>>>>
>>>    I think it is irrelevant to tuning procedure.
>>>
>>>    Our host requires to adjust PHY setting after each time ios setting
>>>    (SDCLK/bus width/speed mode) is changed.
>>>    The simplified sequence is:
>>>    mmc change ios --> mmc_set_ios() --> ->set_ios() --> after sdhci_set_ios(),
>>>    adjust PHY setting.
>>>    During PHY setting adjustment, out host driver has to send commands to
>>>    test current sampling point. Tuning is another independent step.
>>
>> For those speed modes (or other ios changes) that *don't* requires
>> tuning, then what will you do when you send the command to confirm the
>> change of PHY setting and it fails?
>>
>> My assumption is that you will fail anyway, by propagating the error
>> to the mmc core. At least that what was my understanding from your
>> earlier replies, right!?
>>
>> Then, I think there are no point having the host driver sending a
>> command to confirm the PHY settings, as the mmc core will anyway
>> discover if something goes wrong when the next command is sent.
>>
>> Please correct me if I am wrong!
>>
>
>    Sorry that I didn't make myself clear.
>
>    Our host PHY delay line consists of hundreds of sampling points.
>    Each sampling point represents a different phase shift.
>
>    In lower speed mode, our host driver will scan the delay line.
>    It will select and test multiple sampling points, other than testing
>    only single sampling point.
>
>    If a sampling point fails to transfer cmd/data, our host driver will
>    move to test next sampling point, until we find out a group of successful
>    sampling points which can transfer cmd/data. At last we will select
>    a perfect one from them.

Ahh, I see. Unfortunate, this is going to be very hard to implement properly.

The main problem is that the host driver has *no* knowledge about the
internal state of the card, as that is the responsibility of the mmc
core to keep track of.

If the host driver would send a command during every update of the
"ios" setting, from ->set_ios(), for sure it would lead to commands
being sent that are "forbidden" in the current internal state of the
card.
This would lead to that the card initialization sequence fails,
because the card may move to an unknown internal state and the mmc
core would have no knowledge about what happened.

Hmm..

Can you specify, *exactly*, under which "ios updates" you need to
verify updated PHY setting changes by sending a cmd/data? Also, please
specify if it's enough to only test the CMD line or also DATA lines.

Kind regards
Uffe