On Tue, May 23, 2017 at 1:22 PM, Ulf Hansson [off-list ref] wrote:

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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.

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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.

I think for the test module it conceptually makes more sense to
be separate, though I can see that this requires to be careful
with the debugfs file lifetime rules.

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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.

Ok, it's been a while since I looked at the details, thanks for the
clarification.

     Arnd