[Intel-gfx] [PATCH 18/18] drm/i915: add I915_PARAM_HAS_VEBOX to i915_getparam

Ben Widawsky ben at bwidawsk.net
Fri May 31 21:52:03 CEST 2013

On Fri, May 31, 2013 at 08:52:29PM +0200, Daniel Vetter wrote:
> On Tue, May 28, 2013 at 07:22:34PM -0700, Ben Widawsky wrote:
> > From: "Xiang, Haihao" <haihao.xiang at intel.com>
> > 
> > This will let userland only try to use the new ring
> > when the appropriate kernel is present
> > 
> > Signed-off-by: Xiang, Haihao <haihao.xiang at intel.com>
> > Reviewed-by: Damien Lespiau <damien.lespiau at intel.com>
> > Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
> So originally I wanted to take a closer look at the interrupt handling
> changes before merging them. But somehow my brain was notoriously not up
> to the task of reviewing tricky interrupt stuff. Anyway here's my list of
> things I've spotted while applying patches:
> - Unrelated, but spotted while checking interrupt code:
>   ironlake_enable_display_irq is not called with the irq_lock held
>   everywhere, and some are outside of the irq setup/teradown (so real
>   races). Specifically
> commit 8664281b64c457705db72fc60143d03827e75ca9
> Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
> Date:   Fri Apr 12 17:57:57 2013 -0300
>     drm/i915: report Gen5+ CPU and PCH FIFO underruns
>   broke stuff. But I guess a full review of the interrupt handling code
>   should be in order ... At least we should sprinkle assert_spin_locked
>   harder.
> Now the real stuff:
> - rmw register access isn't paranoid, but imo fragile. Either we don't
>   need it, and then it just obfuscates the code (especially with scary
>   comments around). Or there's indeed a race somewhere, and then rmw is
>   _really_ good at papering over it. Until it blows up randomly and no one
>   has a clue why.
>   So I'm not a fan, and I've pretty much exlcusive just killed them. These
>   patches add _lots_ of them instead.
> - rps.lock could just be killed and existing users switched over to
>   irq_lock. Would simplify a lot in the interrupt handling. E.g. the
>   special ring->irqrefcount could just be dropped.
> - rps setup is async now (yeah, that's newer than these patches, still). I
>   think I've seen a few races around that ...
> - There's no inconsistencies in the PM rps interrupt setup on snb vs
>   ivb/hsw. Such inconsistency tend to be fragile (but I haven't spotted
>   something which would blow up on snb).
> - CS_MASTER interrupt handling: None of the other rings seem to enable
>   this on gen5+. Not sure whether it actually works correctly, I suspect
>   at least i915_report_and_clear_eir needs some more code ...
> - Calling queue_work from the spin_lock protection smells a bit like
>   cargo-culting (I've reinstated that one since later patches would have
>   been broken).
> - hsw_pm_irq_handler has no need to unconditionally take the spinlock.
> Patches are merged for now, but I'm not happy by far.
> Cheers, Daniel

Of these, which have you changed/fixed? That way if someone wants to
start addressing the issues, they know where to start.

Ben Widawsky, Intel Open Source Technology Center

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