delayed close on mtdblock

[Joakim Tjernlund]

>
> On Wed, 2012-01-04 at 15:18 +0100, Alexander Stein wrote:
> > Hello,
> >
> > I observed an somewhat interesting situation regarding mtdblock. I have a NOR-
> > Flash with several mtd partitions. One holds the configuration from the
> > bootloader and another one contains UBI/UBIFS.
> > During bootup I attach UBI and mount UBIFS, no problems so far. To read the
> > bootloader coniguration I open the corresponding mtdblock with O_RDONLY, do an
> > lseek, read and close it afterwards, nothing special. But I noticed the
> > close() call take >1s which seems to far big, as there is nothing to be
> > written into this mtdblock device.
> > I digged into the kernel and get to mtdblock_release(). I can see that
> > write_cached_data does nothing as the cache is clean. But mbd->mtd->sync
> > (cfi_amdstd_sync in my case) takes a while because the chip state is currently
> > FL_ERASING. The retry loop is taken several times before exiting the function.
> > If I don't mount UBIFS there is no such delay. I'm wondering if there is
> > actually a need to sync the chip if the cache is clean. Can someone explain
> > this to me?
>
> Most probably this is because NOR flash erase is very slow. You probably
> do writes to the UBIFS partition, which initiates many erase operations.
> When you close the mtdblock device - it syncs the flash chip which
> blocks until the pending erase operations initiated by UBIFS finish
> (because these are 2 partitions on the same chip).
>
> I think the quick fix for you would be to avoid calling mtd->sync() in
> mtdblock if the device is R/O - makes no sense anyway. Care to submit a
> patch?

Me too. I fixed a similar issue for mtdchar "[MTD] Only call mtd->sync() method in mtdchar close if opened for write."
in 2007 so the same should be applied for mtdblock

 Jocke