On 2017/2/7 15:54, Ulf Hansson wrote:
[...]
OK, I see the MMC_CAP_AGGRESSIVE_PM is already checked in the
mmc_runtime_suspend() function, so your approach, do not send
Sleep command on Runtime Suspend, is already supported.
In case the MMC_CAP_AGGRESSIVE_PM is not set, Sleep command
will not be sent, and the device will be able to perform its
AUTO_BKOPS (if needed).
However, as far as I see in modern mobile hosts,
the Sleep is sent on every Suspend, so I assume the
MMC_CAP_AGGRESSIVE_PM is enabled in most of the cases?
Only Intel platforms add this caps on upstreamed kernel tree and
no, AOSP kernel tree didn't change that much either. But I guess
some vendors want aggressive pm policy for their production?
IMHO, the basic concept of mmc stack is that we could provide
the solutions to support different perf & pm policy for folks but
it's their call to decide it by adding these caps there.
I assume you know the consequences of using MMC_CAP_AGGRESSIVE_PM,
still allow me to elaborate a bit on my view.
So, MMC_CAP_AGGRESSIVE_PM tells runtime PM suspend of the card to put
it into sleep/power off, meaning saving power! However, it also means
preventing the eMMC from performing any background operations.
The similar applies to the system PM suspend case, no matter if you
are using MMC_CAP_AGGRESSIVE_PM or not.
To me it seems like we somehow need to start to consider the eMMC'ss
BKOPS status in these paths. Depending on the BKOPS state, we may
abort the sleep/power off things via returning -EBUSY etc, as
otherwise we could end up with poor performing eMMCs, couldn't we!?
Nope, we could. But I just wonder how *aggressive* folks wanted.. Do
they would rather sacrificing the performace to save more power when
adding this caps before?
To me, things like this didn't always exist the "best choice", but we
could find a "better choice". :)
Kind regards
Uffe
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