Allow opal-async waiters to get interrupted

V5: Address review from Boris Brezillon, thanks! Minor cleanups and descriptions - no functional changes.

V4: Rework and rethink.

To recap:
Userspace MTD read()s/write()s and erases to powernv_flash become calls into the OPAL firmware which subsequently handles flash access. Because the read()s, write()s or erases can be large (bounded of course my the size of flash) OPAL may take some time to service the request, this causes the powernv_flash driver to sit in a wait_event() for potentially minutes. This causes two problems, firstly, tools appear to hang for the entire time as they cannot be interrupted by signals and secondly, this can trigger hung task warnings. The correct solution is to use wait_event_interruptible() which my rework (as part of this series) of the opal-async infrastructure provides.

The final patch in this series achieves this. It should eliminate both hung tasks and threads locking up.

Included in this series are other simpler fixes for powernv_flash:

Don't always return EIO on error. OPAL does mutual exclusion on the flash and also knows when the service processor takes control of the flash, in both of these cases it will return OPAL_BUSY, translating this to EIO is misleading to userspace.

Handle receiving OPAL_SUCCESS when it expects OPAL_ASYNC_COMPLETION and don't treat it as an error. Unfortunately there are too many drivers out there with the incorrect behaviour so this means OPAL can never return anything but OPAL_ASYNC_COMPLETION, this shouldn't prevent the code from being correct.

Don't return ERESTARTSYS if token acquisition is interrupted as powernv_flash can't be sure it hasn't already performed some work, let userspace deal with the problem.

Change the incorrect use of BUG_ON() to WARN_ON() in powernv_flash.

Not for powernv_flash, a fix from Stewart Smith which fits into this series as it relies on my improvements to the opal-async infrastructure.

V3: export opal_error_code() so that powernv_flash can be built=m

Hello,

Version one of this series ignored that OPAL may continue to use buffers passed to it after Linux kfree()s the buffer. This version addresses this, not in a particularly nice way - future work could make this better. This version also includes a few cleanups and fixups to powernv_flash driver one along the course of this work that I thought I would just send.

The problem we're trying to solve here is that currently all users of the opal-async calls must use wait_event(), this may be undesirable when there is a userspace process behind the request for the opal call, if OPAL takes too long to complete the call then hung task warnings will appear.

In order to solve the problem callers should use wait_event_interruptible(), due to the interruptible nature of this call the opal-async infrastructure needs to track extra state associated with each async token, this is prepared for in patch 6/10.

While I was working on the opal-async infrastructure improvements Stewart fixed another problem and he relies on the corrected behaviour of opal-async so I've sent it here.

Hello MTD folk, traditionally Michael Ellerman takes powernv_flash driver patches through the powerpc tree, as always your feedback is very welcome.

Thanks,

Cyril

Cyril Bur (9):
mtd: powernv_flash: Use WARN_ON_ONCE() rather than BUG_ON()
mtd: powernv_flash: Don't treat OPAL_SUCCESS as an error
mtd: powernv_flash: Remove pointless goto in driver init
mtd: powernv_flash: Don't return -ERESTARTSYS on interrupted token
acquisition
powerpc/opal: Make __opal_async_{get,release}_token() static powerpc/opal: Rework the opal-async interface powerpc/opal: Add opal_async_wait_response_interruptible() to
opal-async
powerpc/powernv: Add OPAL_BUSY to opal_error_code()
mtd: powernv_flash: Use opal_async_wait_response_interruptible()

Stewart Smith (1):
powernv/opal-sensor: remove not needed lock

 arch/powerpc/include/asm/opal.h              |   4 +-
 arch/powerpc/platforms/powernv/opal-async.c  | 183 +++++++++++++++++++--------
 arch/powerpc/platforms/powernv/opal-sensor.c |  17 +--
 arch/powerpc/platforms/powernv/opal.c        |   2 +
 drivers/mtd/devices/powernv_flash.c          |  83 +++++++-----
 5 files changed, 194 insertions(+), 95 deletions(-)

2.15.0