Re: [PATCH 5/6] mmc: debugfs: Move card status retrieveal into the block layer

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[...]

>>>> +#if IS_ENABLED(CONFIG_MMC_BLOCK)
>>>
>>> What wrong with a regular ifdefs stubs? Why do you need IS_ENABLED()?
>>
>> This is because the entire block layer can be compiled as a
>> module.
>
> The block layer cannot be a module, but the MMC layer can.
>
>> I'm all for making CONFIG_MMC_BLOCK into a bool... but
>> don't know how people (Intel laptops) feel about that extra
>> code in their kernel at all times.
>
> I think CONFIG_MMC should remain tristate. However, we could
> consider making CONFIG_MMC_BLOCK a 'bool' symbol and
> linking it into the mmc-core module when enabled.

That is a good idea, no matter what. We should do the same thing for
CONFIG_MMC_TEST. There are really no need to have to separate modules,
one is more than enough.

However, I don't think that by itself, solves the changed life-cycle
issue of the card debugfs node.

Some more protection is needed, to make sure the mmc block device is
loaded/probed before calling mmc_blk_card_status_get().

>
>>> It seems like the life cycle of the card debugfs node is now being
>>> controlled as when the mmc block device driver has been successfully
>>> probed. We need to deal with that somehow.
>>
>> Only for these two files but yes.
>>
>> ext_csd is a bit dubious as it is only available on storage devices
>> (eMMC) that can not be SD, SDIO or combo cards, and we could make
>> it only appear if using the block layer.
>>
>> The card status however we need to keep if people want it.
>>
>> We *COULD* consider just thrashing these debugfs files. It is not
>> technically ABI and I wonder who is actually using them.
>
> I think the ext_csd is extremely useful on storage devices to have
> exposed to user space in some form. There is a comment saying
> that we don't store it in RAM at the moment as it is rarely used,
> but we could change that, as it's only 512 bytes per eMMC device
> and there is rarely more than one of them. IIRC, the ext_csd is
> entirely readonly and doesn't change during runtime, so we
> gain nothing by issuing the commands every time someone reads
> the debugfs file.

First, we have mmc utils (going via mmc ioctl), which purpose are
exactly for these cases. As a matter of fact it does a better job,
since it even present the data in a more human readable format.

Second, ext csd gets updated very often to control/change some
behavior of the device. You must be mixing this up with some of the
other card registers.

Kind regards
Uffe
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