Re: [PATCH] drm/i915: Implement workaround for broken CS tlb on i830/845

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Dec 17, 2012 at 04:46:17PM +0200, Ville Syrjälä wrote:
> On Mon, Dec 17, 2012 at 02:43:03PM +0100, Daniel Vetter wrote:
> > On Mon, Dec 17, 2012 at 01:33:01PM +0000, Chris Wilson wrote:
> > > On Sun, 16 Dec 2012 22:46:00 +0000, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > > > @@ -1087,6 +1087,9 @@ i915_error_first_batchbuffer(struct drm_i915_private *dev_priv,
> > > >  	if (!ring->get_seqno)
> > > >  		return NULL;
> > > >  
> > > > +	if (HAS_BROKEN_CS_TLB(dev_priv->dev))
> > > > +		return i915_error_object_create(dev_priv, ring->private);
> > > 
> > > Hmm, this is complicated by userspace opting out of the CS w/a, and
> > > imposes quite a burden upon our simple seq interface.
> > 
> > Right, I've written this without userspace being able to opt out in mind
> > ... for the seq -ENOMEM, I guess it's just time to bite the bullet. Loads
> > of the error_states for the ilk fallout couldn't be dumped (but could be
> > captured) by bug reporters already :(
> 
> Assuming you're talking about debugfs error_state returning -ENOMEM due
> to seq_file's massive kmalloc(), I had a couple of ideas for fixing it
> in seq_file itself.
> 
> 1) just use vmalloc()
> 
> 2) use multiple pages instead of one big allocation
> 
>  seq_printf() {
>    try to print the line
>    if not enough space {
>      mark the end of valid data in current page
>      allocate a new page
>      print again
>    }
>  }
> 
> And adjust seq_read()/seq_lseek accordingly.
> 
> Of course then you can't print anything > PAGE_SIZE,
> but that seems unlikely anyway, and if really needed
> it could try to allocate something larger than a page
> when needed.

Afaik that's pretty much what the real seq_file interface does, we just
need to port the error state dump code over from the simple_seq_file to
the real one. But since seq_file is designed for more regular stuff, this
will be a slight pain, so I've tried to avoid this ... It sounds like I'm
running low on excuses ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch