[Intel-gfx] drm/i915: Watchdog timeout: IRQ handler for gen8+

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-01-07 12:58:39)
> 
> On 07/01/2019 12:16, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2019-01-07 11:58:13)
> >> On 05/01/2019 02:39, Carlos Santa wrote:
> >>> +static void gen8_watchdog_irq_handler(unsigned long data)
> >>> +{
> >>> +     struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
> >>> +     struct drm_i915_private *dev_priv = engine->i915;
> >>> +     enum forcewake_domains fw_domains;
> >>> +     u32 current_seqno;
> >>> +
> >>> +     switch (engine->id) {
> >>> +     default:
> >>> +             MISSING_CASE(engine->id);
> >>> +             /* fall through */
> >>> +     case RCS:
> >>> +             fw_domains = FORCEWAKE_RENDER;
> >>> +             break;
> >>> +     case VCS:
> >>> +     case VCS2:
> >>> +     case VECS:
> >>> +             fw_domains = FORCEWAKE_MEDIA;
> >>> +             break;
> >>> +     }
> >>> +
> >>> +     intel_uncore_forcewake_get(dev_priv, fw_domains);
> >>
> >> I'd be tempted to drop this and just use I915_WRITE. It doesn't feel
> >> like there is any performance to be gained with it and it embeds too
> >> much knowledge here.
> > 
> > No, no, no. Let's not reintroduce a fw inside irq context on a frequent
> > timer again.
> 
> Tasklet and hopefully watchdog timeouts are not frequent. :)

I thought the typical value mentioned elsewhere was a 1ms watchdog. Some
might say why even use a watchdog for longer than that as a hrtimer will
be more efficient (coupling in with other timer activity) ;)
-Chris