Re: [PATCH V5 02/15] mmc: core: Enable / disable re-tuning

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[...]

>>>> 1) Card removal/detect (hold/release?)
>>>
>>> Re-tuning will be done if needed before detect (because it is done before a
>>> request), which is necessary because detect can fail if tuning is needed.
>>>
>>> Re-tuning is done before a request. Requests aren't started if the card has
>>> been removed i.e. mmc_start_request() calls mmc_card_removed()
>>>
>>> If tuning is executed while a card is being removed, then the tuning will
>>> fail and the request will be errored out.
>>
>> So you are saying that we instead of relying on the CMD13 (for SD/MMC)
>> to check whether the card is still alive, it's fine to trigger a
>> re-tuning instead.
>
> (Oops forgot to answer this one, sorry)
>
> Yes, why not?
>
>>
>> I don't think that is an effective way to remove a card.
>
> Generally we know the card is removed from card-detect so no commands are
> sent in either case.

Not sure what you mean here.

In case when the card is "idle" and the host sees a GPIO CD irq, it
will trigger a detect work to run mmc_rescan().

In this case, it's the responsibility of mmc_rescan() to find out if
the card is being removed. It does so by invoking the
bus_ops->detect() callback, which eventually will send a CMD13 for
mmc/sd.

In this scenario, I can't see why we want to allow re-tuning to happen
in front of the CMD13 command.

>
>>
>> Moreover, I find it quite unreasonable to say the check for an alive
>> card, would fail because of that a re-tuning is needed. That would in
>> principle mean that we never should be able to hold re-tune for any
>> commands sequences.
>
> Re-tuning must work if the card is alive. CMD13 might get a CRC error if
> re-tuning is needed.

And that then applies to all commands which we hold re-tuning for. So
then we can't _ever_  hold re-tuning for any command, since we might
get CRC errors.

Kind regards
Uffe
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