Sebastian Rasmussen wrote:
Hi!
Err, no. You're not allowed to power down the card between commands
unless the card has been removed or been has finished with.
If you power down the card (which you _are_ doing by writing zero to
the MMCIPOWER register), then you have to do a full setup of the card
when you resume.
MCIPower is according to ARM PL180 TRM signalling to an external power
supply to turn on/off (MCIPWR), whether to use open-drain (MCIROD),
what voltage to use (MCIVDD) and whether the card is clocked (MCICLK).
According ST-Ericsson's public PL180 derivative spec[1] it seems to work
roughly in same way (but renaming the register SDI_PWR and the signals
SDIPWR & SDICLK). However, there is no SDIVDD as the derivative can not
signal desired voltage level externally (there are no bits in SDI_PWR for this).
This makes it plausible that SDIPWR may not be routed externally either.
Can you verify this as there are no signal routing diagrams in the spec..?
The hole idea with this PM patch is to make sure the vcore regulator and
the clock are disabled in runtime_suspend to be able to save a huge
amount of current in "idle" mode.
Disabling the vcore regulator will sooner or later (depending on your
regulator tree) mean that that power to the controller is actually cut,
which then means that all registers will be "cleared" including the
MCIPWR. So the actual reason for clearing the registers in the
runtime_suspend function is because of two reasons.
1. Set the controller in a known state so no "magic" things happens when
we are runtime suspended, for example getting an IRQ.
2. Save power by disabling the clock etc. The actual power to the
controller does not have to be cut just because we have disabled the
vore regulator.
If the ARM PL180 TRM prevent us from from doing this kind of operations
in runtime_suspend, we must think of an alternative solution which just
apply for ST-Ericssons derivative of PL180. THIS IS VERY IMPORTANT to be
able to implement a proper power management solution.
Please check this Russell, this is VERY IMPORTANT!
This leads me to believe that writing 0 to SDI_PWR/MMC in actual practice
doesn't really do much but disabling the clock to the card (and for
ST-Ericsson's PL180, disable direction signalling to the external level
shifter). Clearing bit 8 of MCIClock/SDI_CLKCR also disables the clock.
I guess the patch would appeal more to Russell if mmci_runtime_suspend()
only cleared MCIMask0/SDI_MASK0 and MCIClock/SDI_CLKCR and left
MCIPower/SDI_PWR unchanged. It may be the case that the signal direction
bits need to be cleared for the ST-Ericsson PL180, but I haven't yet verified
this on my Snowball dev board yet.
This is according the comment above not feasible, since the vcore
regulator to the controller is disabled all registers will be "cleared"
anyway.
/ Sebastian
[1] http://www.stericsson.com/developers/DM00030004_AP9500_reference_manual_rev1.pdf
BR
Ulf Hansson
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