Re: [PATCH] dma-fence: add get_signaled_timestamp to fence ops

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Sep 17, 2020 at 02:45:38PM -0700, Veera Sundaram Sankaran wrote:
> Add an optional fence ops to allow drivers to be able to set the
> timestamp for a fence. Some drivers have hardware capability to get
> the precise timestamp of certain events based on which the fences
> are triggered. This allows it to set accurate timestamp factoring
> out any software and IRQ latencies. The get_signaled_timestamp ops,
> if defined by the driver would be used during fence signaling to set
> the timestamp, before setting the flag DMA_FENCE_FLAG_TIMESTAMP_BIT.
> If the callback is not defined, ktime_get is used to set the fence
> timestamp.
> 
> Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>

We don't add hooks without implementations, please submit a complete patch
series (and yes that would need to be with upstream drm/msm drivers if
this is for qcom platforms).

Thanks, Daniel

> ---
>  drivers/dma-buf/dma-fence.c |  6 +++++-
>  include/linux/dma-fence.h   | 13 +++++++++++++
>  2 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 43624b4..95c6ab0 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -4,6 +4,7 @@
>   *
>   * Copyright (C) 2012 Canonical Ltd
>   * Copyright (C) 2012 Texas Instruments
> + * Copyright (c) 2020 The Linux Foundation. All rights reserved.
>   *
>   * Authors:
>   * Rob Clark <robdclark@gmail.com>
> @@ -340,7 +341,10 @@ int dma_fence_signal_locked(struct dma_fence *fence)
>  	/* Stash the cb_list before replacing it with the timestamp */
>  	list_replace(&fence->cb_list, &cb_list);
>  
> -	fence->timestamp = ktime_get();
> +	if (fence->ops->get_signaled_timestamp)
> +		fence->timestamp = fence->ops->get_signaled_timestamp(fence);
> +	else
> +		fence->timestamp = ktime_get();
>  	set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
>  	trace_dma_fence_signaled(fence);
>  
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 09e23ad..ce73aba 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -4,6 +4,7 @@
>   *
>   * Copyright (C) 2012 Canonical Ltd
>   * Copyright (C) 2012 Texas Instruments
> + * Copyright (c) 2020 The Linux Foundation. All rights reserved.
>   *
>   * Authors:
>   * Rob Clark <robdclark@gmail.com>
> @@ -261,6 +262,18 @@ struct dma_fence_ops {
>  	 */
>  	void (*timeline_value_str)(struct dma_fence *fence,
>  				   char *str, int size);
> +
> +	/**
> +	 * @get_signaled_timestamp:
> +	 *
> +	 * Allows the driver to fill in precise timestamp for a fence.
> +	 * This ops would be used during fence signalling to set the timestamp,
> +	 * before setting the flag DMA_FENCE_FLAG_TIMESTAMP_BIT.
> +	 *
> +	 * This callback is optional. If this callback is not present,
> +	 * ktime_get is used to fill in the timestamp.
> +	 */
> +	ktime_t (*get_signaled_timestamp)(struct dma_fence *fence);
>  };
>  
>  void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
> -- 
> 2.7.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch