Re: [RFC PATCH] falconide: remove needless ST-DMA locking

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Saturday 18 October 2008, Bartlomiej Zolnierkiewicz wrote:
> On Saturday 18 October 2008, Geert Uytterhoeven wrote:
> > On Sat, 18 Oct 2008, Michael Schmitz wrote:
> > > > While working on ide_do_request() improvements I stumbled upon
> > > > mismatched ide_get_lock() / ide_release_lock() calls.
> > > > 
> > > > [ It seems to be known issue:
> > > >  http://marc.info/?l=linux-m68k&m=121423752829622&w=2 ]
> > > 
> > > It is a known issue, and I submitted a simple fix to Geert a month or so ago.
> > > It involves moving the ide_get_lock call inside the request loop instead of
> > > doing it once at the start of the function.
> > 
> > See http://marc.info/?l=linux-ide&m=121473433631934&w=2
> > 
> > In response to this patch, I wondered:
> > 
> > > > If hwgroup->busy serves a similar purpose to falconide_intr_lock, what
> > > > about
> > > > moving the setting/clearing of hwgroup->busy into
> > > > ide_{get,release}_lock()
> > > > (and possibly renaming ide_{get,release}_lock() to e.g.
> > > > ide_hwgroup_{set,clear}_busy())?
> > > > 
> > > > What about the other places where hwgroup->busy is set/cleared?
> > 
> > And Michael responsed:
> > 
> > > Uh - that's where it gets a bit sticky again. hwgroup->busy is set and
> > > cleared quite a lot 'preemptively' all over ide-io.c, f.e. in timeout
> > > handling. I'm not sure
> > > whether this would just reintroduce the bug message.
> > > 
> > > The lock must be held as long as there are any interrupts to be expected
> > > from IDE. If the hwgroup->busy semantics reflects just that, it's worth
> > > a try.
> > 
> > Bart, can you shed a light on the hwgroup->busy semantics?
> 
> hwgroup->busy means that hwgroup is busy ;-)
> 
> It protects against any access to the underlying hardware so it is
> also used when device is accessed in polling mode (without waiting
> for IRQ).  However your proposal still sounds fine.  We can treat
> hwgroup->busy as "waiting for IRQ" flag on Falcon and it would be
> correct (we will just hold the lock needlessly sometimes but we're
> already doing exactly that).
> 
> [ The one thing that we have to watch out is not to leak IDE core
>   specific things to <asm/ide.h> and host/platform specific ones to
>   IDE core so some new abstraction level may be needed for handling
>   ST-DMA lock itself (->[un]lock_host methods in struct ide_port_ops
>   or something along the lines)... ]

Since there was no follow-ups on this I've just applied Michael's
patch for now (& will push it to Linus for .28)...