Re: [PATCH] drm/xe/guc: Add more GuC CT states

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Dec 27, 2023 at 12:22:07PM +0530, Riana Tauro wrote:
> 
> 
> On 12/22/2023 11:22 AM, Matthew Brost wrote:
> > On Fri, Dec 22, 2023 at 05:47:17AM +0000, Matthew Brost wrote:
> > > On Thu, Dec 21, 2023 at 01:56:33PM -0800, Daniele Ceraolo Spurio wrote:
> > > > 
> > > > 
> > > > On 12/19/2023 9:28 AM, Matthew Brost wrote:
> > > > > The Guc CT has more than enabled / disables states rather it has 4. The
> > > > > 4 states are not initialized, disabled, drop messages, and enabled.
> > > > > Change the code to reflect this. These states will enable proper return
> > > > > codes from functions and therefore enable proper error messages.
> > > > 
> > > > Can you explain a bit more in which situation we expect to drop messages and
> > > > handle it? AFAICS not all callers waiting for a G2H reply can cope with the
> > > 
> > > Anything that requires a G2H reply must be able to cope with it getting
> > > dropped as the GuC can hang at any moment. Certainly all of submission
> > > is designed this way, so is TLB invalidations. More on that below. With
> > > everything being able to cope with lost G2H their is not a point to
> > > continue to process G2H once a reset has started (or send H2G either).
> > > 
> > > > reply not coming; e.g. it looks like xe_gt_tlb_invalidation_wait() will
> > > 
> > > During a GT reset xe_gt_tlb_invalidation_reset() is called which will
> > > signal all waiters for invalidations avoiding timeouts.
> > > 
> > > So the flow roughly is:
> > > 
> > > Set CT channel to drop messages
> > > Stop all submissions
> > > Do reset
> > > Signal TLB invalidation waiters.
> > > 
> > 
> > Ah, forgot a key detail here. Setting CT channel to drop message before
> > do the reset is key here - we don't want a G2H being processed to race
> > with cleaning up lost G2H in there reset step.
> > 
> > Matt
> > 
> > > > timeout and throw an error (which IMO is already an issue, because the reply
> > > > might be lost due to reset). I know that currently in all cases in which we
> > > > stop communication we do a reset, so the situation ends up ok, but there is
> > > > a pending series to remove the reset in the runtime suspend/resume scenario
> > > > (https://patchwork.freedesktop.org/series/122772/) in which case IMO we
> > > 
> > > This path we would want to put the GuC communication into a state where
> > > if messages send / recv this triggers an error. (-ENODEV).  We don't
> > > expect to suspend the device and then send / recv messages. That is the
> > > point of this patch - it is fine drop messages during a reset, not if
> > > during suspend or if CT has not yet been initialized.
> 
> Hi Matthew
> 
> During D3hot->D0 , currently GuC is reloaded during resume. This pending
> patch https://patchwork.freedesktop.org/series/122772/ only suspends/resumes
> CTB communication instead of reload .
> 
> Which states should be used in this case?
> 

I addressed this in my reply to Daniele, see '3. Runtime suspend'.

Matt

> Thanks
> Riana
> > > 
> > > Proper error messages will added based on these new states.
> > > 
> > > > don't want to drop messages but do a flush instead.
> > > > 
> > > 
> > > See above. Also unsure what you mean by flush here? Do you mean the G2H
> > > worker? I think that creates some dma-fencing (or lockdep) nightmares if
> > > we do that.
> > > 
> > > Matt
> > > 
> > > > Daniele
> > > > 
> > > > > 
> > > > > Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
> > > > > Cc: Tejas Upadhyay <tejas.upadhyay@intel.com>
> > > > > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > > > > ---
> > > > >    drivers/gpu/drm/xe/xe_guc.c          |  4 +-
> > > > >    drivers/gpu/drm/xe/xe_guc_ct.c       | 55 ++++++++++++++++++++--------
> > > > >    drivers/gpu/drm/xe/xe_guc_ct.h       |  8 +++-
> > > > >    drivers/gpu/drm/xe/xe_guc_ct_types.h | 18 ++++++++-
> > > > >    4 files changed, 64 insertions(+), 21 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/xe/xe_guc.c b/drivers/gpu/drm/xe/xe_guc.c
> > > > > index 482cb0df9f15..9b0fa8b1eb48 100644
> > > > > --- a/drivers/gpu/drm/xe/xe_guc.c
> > > > > +++ b/drivers/gpu/drm/xe/xe_guc.c
> > > > > @@ -645,7 +645,7 @@ int xe_guc_mmio_send_recv(struct xe_guc *guc, const u32 *request,
> > > > >    	BUILD_BUG_ON(VF_SW_FLAG_COUNT != MED_VF_SW_FLAG_COUNT);
> > > > > -	xe_assert(xe, !guc->ct.enabled);
> > > > > +	xe_assert(xe, !xe_guc_ct_enabled(&guc->ct));
> > > > >    	xe_assert(xe, len);
> > > > >    	xe_assert(xe, len <= VF_SW_FLAG_COUNT);
> > > > >    	xe_assert(xe, len <= MED_VF_SW_FLAG_COUNT);
> > > > > @@ -827,7 +827,7 @@ int xe_guc_stop(struct xe_guc *guc)
> > > > >    {
> > > > >    	int ret;
> > > > > -	xe_guc_ct_disable(&guc->ct);
> > > > > +	xe_guc_ct_drop_messages(&guc->ct);
> > > > >    	ret = xe_guc_submit_stop(guc);
> > > > >    	if (ret)
> > > > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> > > > > index 24a33fa36496..22d655a8bf9a 100644
> > > > > --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> > > > > +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> > > > > @@ -278,12 +278,25 @@ static int guc_ct_control_toggle(struct xe_guc_ct *ct, bool enable)
> > > > >    	return ret > 0 ? -EPROTO : ret;
> > > > >    }
> > > > > +static void xe_guc_ct_set_state(struct xe_guc_ct *ct,
> > > > > +				enum xe_guc_ct_state state)
> > > > > +{
> > > > > +	mutex_lock(&ct->lock);		/* Serialise dequeue_one_g2h() */
> > > > > +	spin_lock_irq(&ct->fast_lock);	/* Serialise CT fast-path */
> > > > > +
> > > > > +	ct->g2h_outstanding = 0;
> > > > > +	ct->state = state;
> > > > > +
> > > > > +	spin_unlock_irq(&ct->fast_lock);
> > > > > +	mutex_unlock(&ct->lock);
> > > > > +}
> > > > > +
> > > > >    int xe_guc_ct_enable(struct xe_guc_ct *ct)
> > > > >    {
> > > > >    	struct xe_device *xe = ct_to_xe(ct);
> > > > >    	int err;
> > > > > -	xe_assert(xe, !ct->enabled);
> > > > > +	xe_assert(xe, !xe_guc_ct_enabled(ct));
> > > > >    	guc_ct_ctb_h2g_init(xe, &ct->ctbs.h2g, &ct->bo->vmap);
> > > > >    	guc_ct_ctb_g2h_init(xe, &ct->ctbs.g2h, &ct->bo->vmap);
> > > > > @@ -300,12 +313,7 @@ int xe_guc_ct_enable(struct xe_guc_ct *ct)
> > > > >    	if (err)
> > > > >    		goto err_out;
> > > > > -	mutex_lock(&ct->lock);
> > > > > -	spin_lock_irq(&ct->fast_lock);
> > > > > -	ct->g2h_outstanding = 0;
> > > > > -	ct->enabled = true;
> > > > > -	spin_unlock_irq(&ct->fast_lock);
> > > > > -	mutex_unlock(&ct->lock);
> > > > > +	xe_guc_ct_set_state(ct, XE_GUC_CT_STATE_ENABLED);
> > > > >    	smp_mb();
> > > > >    	wake_up_all(&ct->wq);
> > > > > @@ -321,12 +329,12 @@ int xe_guc_ct_enable(struct xe_guc_ct *ct)
> > > > >    void xe_guc_ct_disable(struct xe_guc_ct *ct)
> > > > >    {
> > > > > -	mutex_lock(&ct->lock); /* Serialise dequeue_one_g2h() */
> > > > > -	spin_lock_irq(&ct->fast_lock); /* Serialise CT fast-path */
> > > > > -	ct->enabled = false; /* Finally disable CT communication */
> > > > > -	spin_unlock_irq(&ct->fast_lock);
> > > > > -	mutex_unlock(&ct->lock);
> > > > > +	xe_guc_ct_set_state(ct, XE_GUC_CT_STATE_DISABLED);
> > > > > +}
> > > > > +void xe_guc_ct_drop_messages(struct xe_guc_ct *ct)
> > > > > +{
> > > > > +	xe_guc_ct_set_state(ct, XE_GUC_CT_STATE_DROP_MESSAGES);
> > > > >    	xa_destroy(&ct->fence_lookup);
> > > > >    }
> > > > > @@ -493,11 +501,19 @@ static int __guc_ct_send_locked(struct xe_guc_ct *ct, const u32 *action,
> > > > >    		goto out;
> > > > >    	}
> > > > > -	if (unlikely(!ct->enabled)) {
> > > > > +	if (ct->state == XE_GUC_CT_STATE_NOT_INITIALIZED ||
> > > > > +	    ct->state == XE_GUC_CT_STATE_DISABLED) {
> > > > >    		ret = -ENODEV;
> > > > >    		goto out;
> > > > >    	}
> > > > > +	if (ct->state == XE_GUC_CT_STATE_DROP_MESSAGES) {
> > > > > +		ret = -ECANCELED;
> > > > > +		goto out;
> > > > > +	}
> > > > > +
> > > > > +	xe_assert(xe, xe_guc_ct_enabled(ct));
> > > > > +
> > > > >    	if (g2h_fence) {
> > > > >    		g2h_len = GUC_CTB_HXG_MSG_MAX_LEN;
> > > > >    		num_g2h = 1;
> > > > > @@ -682,7 +698,8 @@ static bool retry_failure(struct xe_guc_ct *ct, int ret)
> > > > >    		return false;
> > > > >    #define ct_alive(ct)	\
> > > > > -	(ct->enabled && !ct->ctbs.h2g.info.broken && !ct->ctbs.g2h.info.broken)
> > > > > +	(xe_guc_ct_enabled(ct) && !ct->ctbs.h2g.info.broken && \
> > > > > +	 !ct->ctbs.g2h.info.broken)
> > > > >    	if (!wait_event_interruptible_timeout(ct->wq, ct_alive(ct),  HZ * 5))
> > > > >    		return false;
> > > > >    #undef ct_alive
> > > > > @@ -941,12 +958,18 @@ static int g2h_read(struct xe_guc_ct *ct, u32 *msg, bool fast_path)
> > > > >    	lockdep_assert_held(&ct->fast_lock);
> > > > > -	if (!ct->enabled)
> > > > > +	if (ct->state == XE_GUC_CT_STATE_NOT_INITIALIZED ||
> > > > > +	    ct->state == XE_GUC_CT_STATE_DISABLED)
> > > > >    		return -ENODEV;
> > > > > +	if (ct->state == XE_GUC_CT_STATE_DROP_MESSAGES)
> > > > > +		return -ECANCELED;
> > > > > +
> > > > >    	if (g2h->info.broken)
> > > > >    		return -EPIPE;
> > > > > +	xe_assert(xe, xe_guc_ct_enabled(ct));
> > > > > +
> > > > >    	/* Calculate DW available to read */
> > > > >    	tail = desc_read(xe, g2h, tail);
> > > > >    	avail = tail - g2h->info.head;
> > > > > @@ -1245,7 +1268,7 @@ struct xe_guc_ct_snapshot *xe_guc_ct_snapshot_capture(struct xe_guc_ct *ct,
> > > > >    		return NULL;
> > > > >    	}
> > > > > -	if (ct->enabled) {
> > > > > +	if (xe_guc_ct_enabled(ct)) {
> > > > >    		snapshot->ct_enabled = true;
> > > > >    		snapshot->g2h_outstanding = READ_ONCE(ct->g2h_outstanding);
> > > > >    		guc_ctb_snapshot_capture(xe, &ct->ctbs.h2g,
> > > > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct.h b/drivers/gpu/drm/xe/xe_guc_ct.h
> > > > > index f15f8a4857e0..214a6a357519 100644
> > > > > --- a/drivers/gpu/drm/xe/xe_guc_ct.h
> > > > > +++ b/drivers/gpu/drm/xe/xe_guc_ct.h
> > > > > @@ -13,6 +13,7 @@ struct drm_printer;
> > > > >    int xe_guc_ct_init(struct xe_guc_ct *ct);
> > > > >    int xe_guc_ct_enable(struct xe_guc_ct *ct);
> > > > >    void xe_guc_ct_disable(struct xe_guc_ct *ct);
> > > > > +void xe_guc_ct_drop_messages(struct xe_guc_ct *ct);
> > > > >    void xe_guc_ct_fast_path(struct xe_guc_ct *ct);
> > > > >    struct xe_guc_ct_snapshot *
> > > > > @@ -22,10 +23,15 @@ void xe_guc_ct_snapshot_print(struct xe_guc_ct_snapshot *snapshot,
> > > > >    void xe_guc_ct_snapshot_free(struct xe_guc_ct_snapshot *snapshot);
> > > > >    void xe_guc_ct_print(struct xe_guc_ct *ct, struct drm_printer *p, bool atomic);
> > > > > +static inline bool xe_guc_ct_enabled(struct xe_guc_ct *ct)
> > > > > +{
> > > > > +	return ct->state == XE_GUC_CT_STATE_ENABLED;
> > > > > +}
> > > > > +
> > > > >    static inline void xe_guc_ct_irq_handler(struct xe_guc_ct *ct)
> > > > >    {
> > > > >    	wake_up_all(&ct->wq);
> > > > > -	if (ct->enabled)
> > > > > +	if (xe_guc_ct_enabled(ct))
> > > > >    		queue_work(system_unbound_wq, &ct->g2h_worker);
> > > > >    	xe_guc_ct_fast_path(ct);
> > > > >    }
> > > > > diff --git a/drivers/gpu/drm/xe/xe_guc_ct_types.h b/drivers/gpu/drm/xe/xe_guc_ct_types.h
> > > > > index d814d4ee3fc6..e36c7029dffe 100644
> > > > > --- a/drivers/gpu/drm/xe/xe_guc_ct_types.h
> > > > > +++ b/drivers/gpu/drm/xe/xe_guc_ct_types.h
> > > > > @@ -72,6 +72,20 @@ struct xe_guc_ct_snapshot {
> > > > >    	struct guc_ctb_snapshot h2g;
> > > > >    };
> > > > > +/**
> > > > > + * enum xe_guc_ct_state - CT state
> > > > > + * @XE_GUC_CT_STATE_NOT_INITIALIZED: CT suspended, messages not expected in this state
> > > > > + * @XE_GUC_CT_STATE_DISABLED: CT disabled, messages not expected in this state
> > > > > + * @XE_GUC_CT_STATE_DROP_MESSAGES: CT drops messages without errors
> > > > > + * @XE_GUC_CT_STATE_ENABLED: CT enabled, messages sent / recieved in this state
> > > > > + */
> > > > > +enum xe_guc_ct_state {
> > > > > +	XE_GUC_CT_STATE_NOT_INITIALIZED = 0,
> > > > > +	XE_GUC_CT_STATE_DISABLED,
> > > > > +	XE_GUC_CT_STATE_DROP_MESSAGES,
> > > > > +	XE_GUC_CT_STATE_ENABLED,
> > > > > +};
> > > > > +
> > > > >    /**
> > > > >     * struct xe_guc_ct - GuC command transport (CT) layer
> > > > >     *
> > > > > @@ -96,8 +110,8 @@ struct xe_guc_ct {
> > > > >    	u32 g2h_outstanding;
> > > > >    	/** @g2h_worker: worker to process G2H messages */
> > > > >    	struct work_struct g2h_worker;
> > > > > -	/** @enabled: CT enabled */
> > > > > -	bool enabled;
> > > > > +	/** @state: CT state */
> > > > > +	enum xe_guc_ct_state state;;
> > > > >    	/** @fence_seqno: G2H fence seqno - 16 bits used by CT */
> > > > >    	u32 fence_seqno;
> > > > >    	/** @fence_lookup: G2H fence lookup */
> > > >