linux-kernel - Re: [RFC v2 PATCH 5/7] dmaengine: xilinx_dma: Freeup active list based on descriptor completion bit

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Date:   Thu, 15 Apr 2021 09:26:01 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        vkoul@...nel.org, robh+dt@...nel.org, michal.simek@...inx.com
Cc:     dmaengine@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        git@...inx.com
Subject: Re: [RFC v2 PATCH 5/7] dmaengine: xilinx_dma: Freeup active list
 based on descriptor completion bit

On 4/9/21 7:56 PM, Radhey Shyam Pandey wrote:
> AXIDMA IP in SG mode sets completion bit to 1 when the transfer is
> completed. Read this bit to move descriptor from active list to the
> done list. This feature is needed when interrupt delay timeout and
> IRQThreshold is enabled i.e Dly_IrqEn is triggered w/o completing
> interrupt threshold.
>
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> ---
> - Check BD completion bit only for SG mode.
> - Modify the logic to have early return path.
> ---
>   drivers/dma/xilinx/xilinx_dma.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index 890bf46b36e5..f2305a73cb91 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -177,6 +177,7 @@
>   #define XILINX_DMA_CR_COALESCE_SHIFT	16
>   #define XILINX_DMA_BD_SOP		BIT(27)
>   #define XILINX_DMA_BD_EOP		BIT(26)
> +#define XILINX_DMA_BD_COMP_MASK		BIT(31)
>   #define XILINX_DMA_COALESCE_MAX		255
>   #define XILINX_DMA_NUM_DESCS		512
>   #define XILINX_DMA_NUM_APP_WORDS	5
> @@ -1683,12 +1684,18 @@ static void xilinx_dma_issue_pending(struct dma_chan *dchan)
>   static void xilinx_dma_complete_descriptor(struct xilinx_dma_chan *chan)
>   {
>   	struct xilinx_dma_tx_descriptor *desc, *next;
> +	struct xilinx_axidma_tx_segment *seg;
>   
>   	/* This function was invoked with lock held */
>   	if (list_empty(&chan->active_list))
>   		return;
>   
>   	list_for_each_entry_safe(desc, next, &chan->active_list, node) {
> +		/* TODO: remove hardcoding for axidma_tx_segment */
> +		seg = list_last_entry(&desc->segments,
> +				      struct xilinx_axidma_tx_segment, node);
> +		if (!(seg->hw.status & XILINX_DMA_BD_COMP_MASK) && chan->has_sg)
> +			break;
>   		if (chan->has_sg && chan->xdev->dma_config->dmatype !=
>   		    XDMA_TYPE_VDMA)
>   			desc->residue = xilinx_dma_get_residue(chan, desc);

Since not all descriptors will be completed in this function the 
`chan->idle = true;` in xilinx_dma_irq_handler() needs to be gated on 
the active_list being empty.

xilinx_dma_complete_descriptor