Re: core: negotiate ocr during resume

[Prasanna NAVARATNA <prasanna.navaratna@gmail.com>]

Kevin : you didn't handle the special case that the card is changed to a
new card during suspended. So the ocr may be different here.

PNN : This case doesn't holds good because even when new card is inserted
during suspend, cd interrupt is generated and mmc_detect_change will be
called and mmc_rescan will be scheduled to begin initialization from the
beginning, where ocr is freshly read from new card (mmc_attach_***) and my
patch will take care to update new ocr in card->ocr.
Although consider an hypothetical situation where within the debounce time
of cd, suppose resume gets called, it may fail. But fair enough after 200ms,
fresh initialization will begin and card re-inits. So no need to take
special consideration here. Don't you agree?

Kevin : But if the card detect can't wakeup system then the cd interrupt may
be discarded if it occurred during system suspended. For example, if
the card detect used slot-gpio and the slot power is off during system
suspended or card used polling for card detect.
So there must be a solution to verify whether a same card after system
resumed. In fact, there have been such method in current code:

in mmc_sd_init_card:
        if (oldcard) {
                if (memcmp(cid, oldcard->raw_cid, sizeof(cid)) != 0)
                        return -ENOENT;
                card = oldcard;

So in my patch, I moved mmc_select_voltage after this verification.
Please consider this case.

_PNN_ : I personally haven’t seen any system design where card insertion or 
removal doesn't generate interrupt to resume the system (I may not have seen 
enough variety of systems)
But suppose assume, mmc_detect_change, for various reasons as you mentioned 
above is not called during card insertion or removal.
Then still “oldcard” pointer is valid but old card has been replaced with 
new card. Your patch will still consider old ocr saved of old card. Right?
I didn't understand, how does your patch works and takes care of this 
situation? Please elaborate.

Thanks & Regards,
Prasanna NAVARATNA