Ulf,

On Tue, Jan 27, 2015 at 7:18 AM, Ulf Hansson [off-list ref] wrote:

quoted

I asked Addy to post upstream against mmc_send_tuning(), but I guess
he didn't (he posted against Alex's NAKed patch instead).

...when I talked to him about it, Addy was asserting that when tuning
fails it is important (at least on dw_mmc on rk3288) that we wait for
the card to stop being busy and that the way to detect was using
mmc_send_status().

So, could that be due to the internal logic of the error handling in
dw_mmc driver? Or you think this is a generic issue?

According to the specifications (eMMC and SD) both states that the
tuning command has an R1 response. So, there shouldn't be any busy
signalling involved - at least according to spec.

I did a bit of digging into this issue myself.  What I found was that
a "response CRC" and "end of transfer".  This was why I posted up
<https://patchwork.kernel.org/patch/5623071/>.  From that patch:

Specifically it looks like in certain error conditions (I saw this
with Response CRC errors) that data keeps showing up in the FIFO even
after the error is reported and the CD (command done) bit is set.  If
we don't wait for this data to finish transferring then it confuses
the next transaction.  In the specific failure case I ran into I found
that I could monitor the data_state_mc_busy bit and wait for it to
clear, but in other failure cases this bit was stuck at busy when we
saw an error.  Hence a generic big delay seems like the only option.

...Addy instead fixed the problem using mmc_send_status() to try to
detect when the transfer was all done and it apparently worked, but it
seemed odd to me.  My MMC "expertise" pretty much ends with looking
for simple logic errors in the MMC driver, so my hope was that one of
you guys would know this better...

quoted

That would mean that against upstream you'd need to change
mmc_send_tuning() to take in the card as well (or move the "host->card
= card" assignment to before UHS init, which seems less desirable?)

What do you think about that?  Is there a better solution?

Why do we need to change mmc_send_tuning()? I thought the issue was
that mmc_send_status(), which currently takes "card" as a parameter.

Well, if mmc_send_tuning() needed to call mmc_send_status() then
mmc_send_tuning() would need the card parameter, right?


Doug