[RFC PATCH 18/97] drm/i915/guc: Don't receive all G2H messages in irq handler

[Matthew Brost]

On Thu, May 06, 2021 at 12:13:32PM -0700, Matthew Brost wrote:
> From: Michal Wajdeczko <michal.wajdeczko at intel.com>
> 
> In irq handler try to receive just single G2H message, let other
> messages to be received from tasklet.
> 
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 67 ++++++++++++++++-------
>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h |  3 +
>  2 files changed, 50 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> index cb58fa7f970c..d630ec32decf 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> @@ -81,6 +81,7 @@ enum { CTB_SEND = 0, CTB_RECV = 1 };
>  
>  enum { CTB_OWNER_HOST = 0 };
>  
> +static void ct_receive_tasklet_func(unsigned long data);
>  static void ct_incoming_request_worker_func(struct work_struct *w);
>  
>  /**
> @@ -95,6 +96,7 @@ void intel_guc_ct_init_early(struct intel_guc_ct *ct)
>  	INIT_LIST_HEAD(&ct->requests.pending);
>  	INIT_LIST_HEAD(&ct->requests.incoming);
>  	INIT_WORK(&ct->requests.worker, ct_incoming_request_worker_func);
> +	tasklet_init(&ct->receive_tasklet, ct_receive_tasklet_func, (unsigned long)ct);

This function is deprecated. tasklet_setup should be used.
I can fix this up when I post the CTB patches.

>  }
>  
>  static inline const char *guc_ct_buffer_type_to_str(u32 type)
> @@ -244,6 +246,7 @@ void intel_guc_ct_fini(struct intel_guc_ct *ct)
>  {
>  	GEM_BUG_ON(ct->enabled);
>  
> +	tasklet_kill(&ct->receive_tasklet);
>  	i915_vma_unpin_and_release(&ct->vma, I915_VMA_RELEASE_MAP);
>  	memset(ct, 0, sizeof(*ct));
>  }
> @@ -629,7 +632,7 @@ static int ct_read(struct intel_guc_ct *ct, u32 *data)
>  	CT_DEBUG(ct, "received %*ph\n", 4 * len, data);
>  
>  	desc->head = head * 4;
> -	return 0;
> +	return available - len;
>  
>  corrupted:
>  	CT_ERROR(ct, "Corrupted descriptor addr=%#x head=%u tail=%u size=%u\n",
> @@ -665,10 +668,10 @@ static int ct_handle_response(struct intel_guc_ct *ct, const u32 *msg)
>  	u32 status;
>  	u32 datalen;
>  	struct ct_request *req;
> +	unsigned long flags;
>  	bool found = false;
>  
>  	GEM_BUG_ON(!ct_header_is_response(header));
> -	GEM_BUG_ON(!in_irq());
>  
>  	/* Response payload shall at least include fence and status */
>  	if (unlikely(len < 2)) {
> @@ -688,7 +691,7 @@ static int ct_handle_response(struct intel_guc_ct *ct, const u32 *msg)
>  
>  	CT_DEBUG(ct, "response fence %u status %#x\n", fence, status);
>  
> -	spin_lock(&ct->requests.lock);
> +	spin_lock_irqsave(&ct->requests.lock, flags);
>  	list_for_each_entry(req, &ct->requests.pending, link) {
>  		if (unlikely(fence != req->fence)) {
>  			CT_DEBUG(ct, "request %u awaits response\n",
> @@ -707,7 +710,7 @@ static int ct_handle_response(struct intel_guc_ct *ct, const u32 *msg)
>  		found = true;
>  		break;
>  	}
> -	spin_unlock(&ct->requests.lock);
> +	spin_unlock_irqrestore(&ct->requests.lock, flags);
>  
>  	if (!found)
>  		CT_ERROR(ct, "Unsolicited response %*ph\n", msgsize, msg);
> @@ -821,31 +824,55 @@ static int ct_handle_request(struct intel_guc_ct *ct, const u32 *msg)
>  	return 0;
>  }
>  
> +static int ct_receive(struct intel_guc_ct *ct)
> +{
> +	u32 msg[GUC_CT_MSG_LEN_MASK + 1]; /* one extra dw for the header */
> +	unsigned long flags;
> +	int ret;
> +
> +	spin_lock_irqsave(&ct->ctbs.recv.lock, flags);
> +	ret = ct_read(ct, msg);
> +	spin_unlock_irqrestore(&ct->ctbs.recv.lock, flags);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (ct_header_is_response(msg[0]))
> +		ct_handle_response(ct, msg);
> +	else
> +		ct_handle_request(ct, msg);
> +
> +	return ret;
> +}
> +
> +static void ct_try_receive_message(struct intel_guc_ct *ct)
> +{
> +	int ret;
> +
> +	if (GEM_WARN_ON(!ct->enabled))
> +		return;
> +
> +	ret = ct_receive(ct);
> +	if (ret > 0)
> +		tasklet_hi_schedule(&ct->receive_tasklet);
> +}
> +
> +static void ct_receive_tasklet_func(unsigned long data)
> +{

As mentioned above tasklet_init is deprecated. The callback now accepts
the tasklet structure and ct can be looked up via container_of macro.

Everything else looks good.

With that and changing to the new tasklet API:
Reviewed-by: Matthew Brost <matthew.brost at intel.com>

> +	struct intel_guc_ct *ct = (struct intel_guc_ct *)data;
> +
> +	ct_try_receive_message(ct);
> +}
> +
>  /*
>   * When we're communicating with the GuC over CT, GuC uses events
>   * to notify us about new messages being posted on the RECV buffer.
>   */
>  void intel_guc_ct_event_handler(struct intel_guc_ct *ct)
>  {
> -	u32 msg[GUC_CT_MSG_LEN_MASK + 1]; /* one extra dw for the header */
> -	unsigned long flags;
> -	int err = 0;
> -
>  	if (unlikely(!ct->enabled)) {
>  		WARN(1, "Unexpected GuC event received while CT disabled!\n");
>  		return;
>  	}
>  
> -	do {
> -		spin_lock_irqsave(&ct->ctbs.recv.lock, flags);
> -		err = ct_read(ct, msg);
> -		spin_unlock_irqrestore(&ct->ctbs.recv.lock, flags);
> -		if (err)
> -			break;
> -
> -		if (ct_header_is_response(msg[0]))
> -			err = ct_handle_response(ct, msg);
> -		else
> -			err = ct_handle_request(ct, msg);
> -	} while (!err);
> +	ct_try_receive_message(ct);
>  }
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> index bc52dc479a14..cb222f202301 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.h
> @@ -6,6 +6,7 @@
>  #ifndef _INTEL_GUC_CT_H_
>  #define _INTEL_GUC_CT_H_
>  
> +#include <linux/interrupt.h>
>  #include <linux/spinlock.h>
>  #include <linux/workqueue.h>
>  
> @@ -55,6 +56,8 @@ struct intel_guc_ct {
>  		struct intel_guc_ct_buffer recv;
>  	} ctbs;
>  
> +	struct tasklet_struct receive_tasklet;
> +
>  	struct {
>  		u32 last_fence; /* last fence used to send request */
>  
> -- 
> 2.28.0
>