Re-entrancy of flash erase/write

[Robert Kaiser]

On Mon, 25 Feb 2002, David Woodhouse wrote:

> 
> rob at sysgo.de said:
> >  [David, OK to apply this ?] 
> 
> I'd rather it was done in the map driver's set_vpp function itself. 
> Sometimes you have more than one map driver, because you have different 
> regions of flash - but they all share the same Vpp control. In which case 
> you need to do the counting in the map driver anyway. 

Agreed. I'll modify the dilnetpc driver then.

> 
> 
> >  I looked into this a little further: it seems that the erase
> > functions in cfi_cmdset_000?.c and amd_flash.c temporarily release the
> > chip->mutex while VPP is on. Won't that allow other threads to get
> > hold of the mutex and fiddle with VPP, possibly turning it off ? 
> 
> I see the possibility, but surely that would only _actually_ happen if we 
> started to support writes during erase suspend? Otherwise, the only thing 
> that should happen during an erase is a _read_, which doesn't set and clear 
> vpp.

What mechanism is there to avoid writes during erase suspend ? I have
seen the problem in situations where the JFFS2 GC thread was erasing
while another process (tar in my case) was writing to a *different
partition* in the same chip. (Maybe that is a hint ?) Introducing the 
set_vpp counter reliably solved this.

Rob

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Robert Kaiser                          email: rkaiser at sysgo.de
SYSGO RTS GmbH
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