linux-kernel - Re: [PATCH v4 05/15] dmaengine: Add support for reporting DMA cached data amount

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Date:   Mon, 11 Nov 2019 10:09:57 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     robh+dt@...nel.org, nm@...com, ssantosh@...nel.org,
        dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, grygorii.strashko@...com,
        lokeshvutla@...com, t-kristo@...com, tony@...mide.com,
        j-keerthy@...com
Subject: Re: [PATCH v4 05/15] dmaengine: Add support for reporting DMA cached
 data amount

On 01-11-19, 10:41, Peter Ujfalusi wrote:
> A DMA hardware can have big cache or FIFO and the amount of data sitting in
> the DMA fabric can be an interest for the clients.
> 
> For example in audio we want to know the delay in the data flow and in case
> the DMA have significantly large FIFO/cache, it can affect the latenc/delay
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> Reviewed-by: Tero Kristo <t-kristo@...com>
> ---
>  drivers/dma/dmaengine.h   | 8 ++++++++
>  include/linux/dmaengine.h | 2 ++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/drivers/dma/dmaengine.h b/drivers/dma/dmaengine.h
> index 501c0b063f85..b0b97475707a 100644
> --- a/drivers/dma/dmaengine.h
> +++ b/drivers/dma/dmaengine.h
> @@ -77,6 +77,7 @@ static inline enum dma_status dma_cookie_status(struct dma_chan *chan,
>  		state->last = complete;
>  		state->used = used;
>  		state->residue = 0;
> +		state->in_flight_bytes = 0;
>  	}
>  	return dma_async_is_complete(cookie, complete, used);
>  }
> @@ -87,6 +88,13 @@ static inline void dma_set_residue(struct dma_tx_state *state, u32 residue)
>  		state->residue = residue;
>  }
>  
> +static inline void dma_set_in_flight_bytes(struct dma_tx_state *state,
> +					   u32 in_flight_bytes)
> +{
> +	if (state)
> +		state->in_flight_bytes = in_flight_bytes;
> +}
> +
>  struct dmaengine_desc_callback {
>  	dma_async_tx_callback callback;
>  	dma_async_tx_callback_result callback_result;
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 0e8b426bbde9..c4c5219030a6 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -682,11 +682,13 @@ static inline struct dma_async_tx_descriptor *txd_next(struct dma_async_tx_descr
>   * @residue: the remaining number of bytes left to transmit
>   *	on the selected transfer for states DMA_IN_PROGRESS and
>   *	DMA_PAUSED if this is implemented in the driver, else 0
> + * @in_flight_bytes: amount of data in bytes cached by the DMA.
>   */
>  struct dma_tx_state {
>  	dma_cookie_t last;
>  	dma_cookie_t used;
>  	u32 residue;
> +	u32 in_flight_bytes;

Should we add this here or use the dmaengine_result()

-- 
~Vinod