When Broadcom SDIO cards are idled they go to sleep and a whole
separate subsystem takes over their SDIO communication. This is the
Always-On-Subsystem (AOS) and it can't handle tuning requests.
Specifically, as tested on rk3288-veyron-minnie (which reports having
BCM4354/1 in dmesg), if I force a retune in brcmf_sdio_kso_control()
when "on = 1" (aka we're transition from sleep to wake) by whacking:
bus->sdiodev->func1->card->host->need_retune = 1
...then I can often see tuning fail. In this case dw_mmc reports "All
phases bad!"). Note that I don't get 100% failure, presumably because
sometimes the card itself has already transitioned away from the AOS
itself by the time we try to wake it up. If I force retuning when "on
= 0" (AKA force retuning right before sending the command to go to
sleep) then retuning is always OK.
NOTE: we need _both_ this patch and the patch to avoid triggering
tuning due to CRC errors in the sleep/wake transition, AKA ("brcmfmac:
sdio: Disable auto-tuning around commands expected to fail"). Though
both patches handle issues with Broadcom's AOS, the problems are
1. We want to defer (but not ignore) asynchronous (like
timer-requested) tuning requests till the card is awake. However,
we want to ignore CRC errors during the transition, we don't want
to queue deferred tuning request.
2. You could imagine that the AOS could implement retuning but we
could still get errors while transitioning in and out of the AOS.
Similarly you could imagine a seamless transition into and out of
the AOS (with no CRC errors) even if the AOS couldn't handle
ALSO NOTE: presumably there is never a desperate need to retune in
order to wake up the card, since doing so is impossible. Luckily the
only way the card can get into sleep state is if we had a good enough
tuning to send it a sleep command, so presumably that "good enough"
tuning is enough to wake us up, at least with a few retries.
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>