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PCI device handling (was: Full-time developer available)

From: Olaf Buddenhagen
Subject: PCI device handling (was: Full-time developer available)
Date: Sat, 19 Sep 2015 01:29:22 +0200
User-agent: Mutt/1.5.23 (2014-03-12)


On Fri, Sep 18, 2015 at 09:14:30PM +0200, Robert Millan wrote:
> El 17/09/15 a les 23:25, Samuel Thibault ha escrit:
> >Robert Millan, le Thu 17 Sep 2015 21:55:32 +0200, a écrit :

> >>My understanding is there's no need for an arbiter / multiplexer
> >>as long as all the code playing with PCI devices is well-aware of its 
> >>limits.
> >
> >Yes, for the daily work, the driver can behave well. But to know where
> >the PCI registers are, you need to read that from the config. And that
> >includes unsafe concurrent accesses (i.e. write to a register, read the
> >value). See inside libpciaccess, x86_pci.c which does inl(); outl();
> >inl(); outl();
> Ah, I see what you mean. This seems like a bug in libpciaccess... the routines
> aren't even thread-safe!
> It looks like a generic problem, affecting all uses of libpciaccess (on other
> OS too). I guess it's been tolerated so far because there isn't any readily
> available solution.

Note that the original purpose of libpciaccess was to get rid of
register poking in the X server, and use proper system-provided PCI
access methods instead.

The register poking backend was added after all (after some initial
reservations) for the sake of the Hurd, because we just don't *have* a
proper PCI access method yet... That's a kludge, though -- the plan
always has been to implement a proper PCI server in the Hurd at some
point, and then to provide a libpciaccess backend to access it.

Same for other systems using the register-poking backend.


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