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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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.

-- 
Ville Syrjälä
Intel OTC