[Intel-gfx] [PATCH 51/53] drm/i915/bdw: Document Logical Rings, LR contexts and Execlists

[Daniel Vetter]

On Tue, Jun 17, 2014 at 08:22:55AM +0000, Mateo Lozano, Oscar wrote:
> 
> > -----Original Message-----
> > From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel
> > Vetter
> > Sent: Monday, June 16, 2014 6:56 PM
> > To: Mateo Lozano, Oscar
> > Cc: Chris Wilson; intel-gfx at lists.freedesktop.org
> > Subject: Re: [Intel-gfx] [PATCH 51/53] drm/i915/bdw: Document Logical
> > Rings, LR contexts and Execlists
> > 
> > On Mon, Jun 16, 2014 at 03:24:26PM +0000, Mateo Lozano, Oscar wrote:
> > > > -----Original Message-----
> > > > From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
> > > > Sent: Friday, June 13, 2014 5:51 PM
> > > > To: Mateo Lozano, Oscar
> > > > Cc: intel-gfx at lists.freedesktop.org
> > > > Subject: Re: [Intel-gfx] [PATCH 51/53] drm/i915/bdw: Document
> > > > Logical Rings, LR contexts and Execlists
> > > >
> > > > On Fri, Jun 13, 2014 at 04:38:09PM +0100, oscar.mateo at intel.com
> > wrote:
> > > > > +/**
> > > > > + * intel_execlists_ctx_id() - get the Execlists Context ID
> > > > > + * @ctx_obj: Logical Ring Context backing object.
> > > > > + *
> > > > > + * Do not confuse with ctx->id! Unfortunately we have a name
> > > > > +overload
> > > > > + * here: the old context ID we pass to userspace as a handler so
> > > > > +that
> > > > > + * they can refer to a context, and the new context ID we pass to
> > > > > +the
> > > > > + * ELSP so that the GPU can inform us of the context status via
> > > > > + * interrupts.
> > > > > + *
> > > > > + * Return: 20-bits globally unique context ID.
> > > > > + */
> > > >
> > > > Use tag for the ctx id we pass around in hw?
> > > > -Chris
> > >
> > > I also tried other names, like "submission id", but it confuses people
> > > when they search for in the BSpec. Maybe changing ctx->id to ctx->tag,
> > > and leaving id for the hardware?
> > 
> > I think Chris' idea was to reuse the id from the idr for the hw tag. But I guess
> > that fails because our idr is global.
> > 
> > Or I'm totally confused.
> > 
> > I'd vote for hw_ctx_id or something.
> > -Daniel
> 
> In the first version of the series I tried to reuse the id from the idr,
> but that was a bad idea because the id we pass to the hw has to be
> globally unique, while our idr is per file_priv. What I did is adding an
> id field to the file_priv and then generating the hw ctx id by using
> some bits from ctx->id, some from file_priv->id and finally some from
> ring->id (since we multiplex several hw contexts inside our struct
> intel_context). But the ELSP context descriptor only allows 20 bits for
> the id, so I had to limit the maximum number of contexts, files or rings
> artificially (ugly).

Considerations like this should be somewhere in the commit message.
Especially when it's all stuff you've discovered before review started and
hence doesn't have a public record anywhere.

> Another proposal: s/ctx->id/ctx->handle. After all, our ctx->id software construct is just a userspace handle...

Not sure either is clearer really. As long as there's a clear disdinction
between the hw id and the userspace handle I'm ok, maybe augmented with
some comments to explain the struct fields in the header.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch