[Intel-gfx] [PATCH v4 4/6] drm/i915/guc: (re)initialise doorbell h/w when enabling GuC submission

[Yu Dai]

On 04/13/2016 12:46 PM, Dave Gordon wrote:
> On 13/04/16 18:50, Yu Dai wrote:
> >
> >
> > On 04/07/2016 10:21 AM, Dave Gordon wrote:
> >> During a hibernate/resume cycle, the whole system is reset, including
> >> the GuC and the doorbell hardware. Then the system is booted up, drivers
> >> are loaded, etc -- the GuC firmware may be loaded and set running at this
> >> point. But then, the booted kernel is replaced by the hibernated image,
> >> and this resumed kernel will also try to reload the GuC firmware (which
> >> will fail). To recover, we reset the GuC and try again (which should
> >> work). But this GuC reset doesn't also reset the doorbell hardware, so
> >> it can be left in a state inconsistent with that assumed by the driver
> >> and the GuC.
> >>
> >> It would be better if the GuC reset also cleared all doorbell state,
> >> but that's not how the hardware currently works; also, the driver cannot
> >> directly reprogram the doorbell hardware (only the GuC can do that).
> >>
> >> So this patch cycles through all doorbells, assigning and releasing each
> >> in turn, so that all the doorbell hardware is left in a consistent state,
> >> no matter how it was programmed by the previously-running kernel and/or
> >> GuC firmware.
> >>
> >> This patch can be removed if/when the GuC firmware is updated so that it
> >> (re)initialises the doorbell hardware after every firmware (re)load.
> >>
> >> Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/i915_guc_submission.c | 46
> >> +++++++++++++++++++++++++++++-
> >>   1 file changed, 45 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c
> >> b/drivers/gpu/drm/i915/i915_guc_submission.c
> >> index 2fc69f1..f466eab 100644
> >> --- a/drivers/gpu/drm/i915/i915_guc_submission.c
> >> +++ b/drivers/gpu/drm/i915/i915_guc_submission.c
> >> @@ -707,6 +707,50 @@ static void guc_client_free(struct drm_device *dev,
> >>       kfree(client);
> >>   }
> >> +/*
> >> + * Borrow the first client to set up & tear down every doorbell
> >> + * in turn, to ensure that all doorbell h/w is (re)initialised.
> >> + */
> >> +static void guc_init_doorbell_hw(struct intel_guc *guc)
> >> +{
> >> +    struct drm_i915_private *dev_priv = guc_to_i915(guc);
> >> +    struct i915_guc_client *client = guc->execbuf_client;
> >> +    struct guc_doorbell_info *doorbell;
> >> +    uint16_t db_id, i;
> >> +    void *base;
> >> +    int ret;
> >> +
> >> +    base = kmap_atomic(i915_gem_object_get_page(client->client_obj, 0));
> >> +    doorbell = base + client->doorbell_offset;
> >> +    db_id = client->doorbell_id;
> >> +
> >> +    for (i = 0; i < GUC_MAX_DOORBELLS; ++i) {
> >> +        i915_reg_t drbreg = GEN8_DRBREGL(i);
> >> +        u32 value = I915_READ(drbreg);
> >> +
> >> +        ret = guc_update_doorbell_id(client, doorbell, i);
> >> +
> >> +        if (((value & GUC_DOORBELL_ENABLED) && (i != db_id)) || ret)
> >> +            DRM_DEBUG_DRIVER("Doorbell reg 0x%x was 0x%x, ret %d\n",
> >> +                drbreg.reg, value, ret);
> >> +    }
> >> +
> >> +    /* Restore to original value */
> >> +    guc_update_doorbell_id(client, doorbell, db_id);
> >> +
> >> +    for (i = 0; i < GUC_MAX_DOORBELLS; ++i) {
> >> +        i915_reg_t drbreg = GEN8_DRBREGL(i);
> >> +        u32 value = I915_READ(drbreg);
> >> +
> >> +        if ((value & GUC_DOORBELL_ENABLED) && (i != db_id))
> >> +            DRM_DEBUG_DRIVER("Doorbell reg 0x%x finally 0x%x\n",
> >> +                        drbreg.reg, value);
> >> +
> >> +    }
> >> +
> >
> > The for loop above is not needed. It can be merged into previous loop by
> > print out new drbreg value (read it again after update_doorbell_id).
> >
> > At this point, only need to check if db_id is correctly enabled or not
> > by print out I915_READ(GEN8_DRBREGL(db_id)).
> >
> > Alex
>
> No, the idea is not to check that the GuC call has *enabled* each
> selected doorbell, but to check that after the end of the first loop,
> and the subsequent restore, all *other* doorbells have been *disabled*.
> We're only *selecting* each doorbell so that we can then *deselect* it
> as a side effect of selecting the next one!
>
> Hence separate loop required ...
>
> .Dave.

This still can be done by backup of previous client->doorbell_id. If it 
is not same as the desired db_id, then make sure it is *disabled* after 
the update.

The real problem here, at least not for now, is that it assumes there is 
only one guc_client. In future, if there is user created guc_client, the 
code doesn't restore doorbell for it.

Alex

> >> +    kunmap_atomic(base);
> >> +}
> >> +
> >>   /**
> >>    * guc_client_alloc() - Allocate an i915_guc_client
> >>    * @dev:    drm device
> >> @@ -971,8 +1015,8 @@ int i915_guc_submission_enable(struct drm_device
> >> *dev)
> >>       }
> >>       guc->execbuf_client = client;
> >> -
> >>       host2guc_sample_forcewake(guc, client);
> >> +    guc_init_doorbell_hw(guc);
> >>       return 0;
> >>   }
> >
>