Hi Shawn,
On Wednesday 05 October 2016 03:07 PM, Shawn Lin wrote:
Hi Ravikumar,
+ Alex,
在 2016/10/3 18:43, Ravikumar Kattekola 写道:
Hi all,
I’ve seen an eMMC failure due to pending background operations on
a certain OMAP device since bkops enable bit was not set.
Further investigation showed me that someone already posted patch to
enable Background operations in kernel based on a host capability
check (Caps2 & BK_OPS_EN)
but was turned down quoting that it should be enabled from user space
using mmc-utils.
Enabling this would add one additional check for exception event in
the response R1 or R1B (only on hosts that explicitly set BK_OPS_EN
in caps2).
But not enabling this could lead to a system failure especially when
the Filesystem is on eMMC and the card stops responding due to
pending critical bkops.
I would like to ask for expert opinion on ‘why is it a bad idea to
enable bkops in kernel?’
Some discussion about the similar topic could be found here:
https://patchwork.kernel.org/patch/9157121/
It’s a one time programmable bit but if it helps in keeping system
functional why not do it?
Actually BKOPS_EN is not OTP bit.. Quoted from Ulf "I don't have any
issue to allow all non-OTP registers bits to be written." So I guess
you could do this, although it needs more discussion there.
In the spec for 4.5, jesd84_B45 it does say not whether the ENABLE bit
is OTP.
But in 5.1 spec, jesd84-b51, it says MANUAL_EN is R/W which means OTP
and readable.
As I read form mmc-utils -help
" mmc bkops enable <device>
Enable the eMMC BKOPS feature on <device>.
NOTE! This is a one-time programmable (unreversible)
change "
But it's persistent EXT_CSD register and we get used to control it from
userspace, which is the policy we have been sticking to when writing to
persistent EXT_CSD registers. I guess that is nothing about "right and
wrong", just a rule for us in case someone wants to set the persistent
bit in kernel but setting other persistent bits from user-space, which
is prone to mess up the mmc core. Or, someone will sent mail to the list
asking "why is it a good idea to enable bkops in kernel" ? :)
So there's no functional problem/reason that stops us from enabling
BKOPS (Manual) in
kernel except for consistency with other persistent registers.
Since not enabling BKOPS could lead to a functional failure /
non-responsive system
at a later point of time I guess this could be exempted.
what do you think?
As user I would choose functional safety and reliability over performance.
Hence it would make sense to have the bkops (at least manual) be enabled
by default,
especially in Automotive applications.
I haven’t measured the performance impact but I don’t see a reason
for major drop because the frequency of critical bkops events would
be less.
Regards,
RK
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Thanks for your response.
Regards,
RK
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