Re: delayed close on mtdblock

[Alexander Stein <alexander.stein@systec-electronic.com>]

On Tuesday 10 January 2012 10:54:35 Artem Bityutskiy wrote:
> 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.

I had somethng like this in mind, but was unsure about possible side effects.

> Care to submit a
> patch?

I would gladly submit a patch, but I don't know where to get the R/O status. 
There is no struct file in this function like in the mtdchar case as Joakim 
wrote.

Best regards,
Alexander
-- 
Dipl.-Inf. Alexander Stein

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