linux-kernel - Re: [PATCH 11/11] dmaengine: dw-edma: Remove struct dw_edma

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Message-ID: <5l2vl7sfnqjylmhve47pyi6tchqkn2n77zskkdisyynfxx3ftp@x55amadqlxph>
Date: Tue, 30 Dec 2025 22:31:28 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Frank Li <Frank.Li@....com>
Cc: Vinod Koul <vkoul@...nel.org>, 
	Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Kishon Vijay Abraham I <kishon@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Christoph Hellwig <hch@....de>, Niklas Cassel <cassel@...nel.org>, dmaengine@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, linux-pci@...r.kernel.org, 
	linux-nvme@...ts.infradead.org, imx@...ts.linux.dev
Subject: Re: [PATCH 11/11] dmaengine: dw-edma: Remove struct dw_edma_chunk

On Fri, Dec 12, 2025 at 05:24:50PM -0500, Frank Li wrote:
> The current descriptor layout is:
> 
>   struct dw_edma_desc *desc
>    └─ chunk list
>         └─ burst[]
> 
> Creating a DMA descriptor requires at least two kzalloc() calls because
> each chunk is allocated as a linked-list node. Since the number of bursts
> is already known when the descriptor is created, this linked-list layer is
> unnecessary.
> 
> Move the burst array directly into struct dw_edma_desc and remove the
> struct dw_edma_chunk layer entirely.
> 
> Use start_burst and done_burst to track the current bursts, which current
> are in the DMA link list.
> 
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
>  drivers/dma/dw-edma/dw-edma-core.c | 130 ++++++++++++-------------------------
>  drivers/dma/dw-edma/dw-edma-core.h |  24 ++++---
>  2 files changed, 57 insertions(+), 97 deletions(-)
> 

[...]

>  static struct dma_async_tx_descriptor *
> @@ -551,8 +499,14 @@ static void dw_hdma_set_callback_result(struct virt_dma_desc *vd,
>  		return;
>  
>  	desc = vd2dw_edma_desc(vd);
> -	if (desc)
> -		residue = desc->alloc_sz - desc->xfer_sz;
> +	residue = desc->alloc_sz;

Now you dereference desc without checking for NULL.

> +
> +	if (desc) {
> +		if (result == DMA_TRANS_NOERROR)
> +			residue -= desc->burst[desc->start_burst - 1].xfer_sz;
> +		else if (desc->done_burst)
> +			residue -= desc->burst[desc->done_burst - 1].xfer_sz;
> +	}
>  
>  	res = &vd->tx_result;
>  	res->result = result;
> @@ -571,7 +525,7 @@ static void dw_edma_done_interrupt(struct dw_edma_chan *chan)
>  		switch (chan->request) {
>  		case EDMA_REQ_NONE:
>  			desc = vd2dw_edma_desc(vd);
> -			if (!desc->chunks_alloc) {
> +			if (desc->start_burst >= desc->nburst) {
>  				dw_hdma_set_callback_result(vd,
>  							    DMA_TRANS_NOERROR);
>  				list_del(&vd->node);
> @@ -936,7 +890,7 @@ int dw_edma_probe(struct dw_edma_chip *chip)
>  		goto err_irq_free;
>  
>  	/* Turn debugfs on */
> -	dw_edma_core_debugfs_on(dw);
> +	//dw_edma_core_debugfs_on(dw);

debug code?

>  
>  	chip->dw = dw;
>  
> diff --git a/drivers/dma/dw-edma/dw-edma-core.h b/drivers/dma/dw-edma/dw-edma-core.h
> index 1930c3bce2bf33fdfbf4e8d99002483a4565faed..ba83c42dee5224dccdf34cec6481e9404a607702 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.h
> +++ b/drivers/dma/dw-edma/dw-edma-core.h
> @@ -46,15 +46,8 @@ struct dw_edma_burst {
>  	u64				sar;
>  	u64				dar;
>  	u32				sz;
> -};
> -
> -struct dw_edma_chunk {
> -	struct list_head		list;
> -	struct dw_edma_chan		*chan;
> -	u8				cb;
> +	/* precalulate summary of previous burst total size */
>  	u32				xfer_sz;
> -	u32                             nburst;
> -	struct dw_edma_burst            burst[] __counted_by(nburst);
>  };
>  
>  struct dw_edma_desc {
> @@ -66,6 +59,12 @@ struct dw_edma_desc {
>  
>  	u32				alloc_sz;
>  	u32				xfer_sz;
> +
> +	u32				done_burst;
> +	u32				start_burst;
> +	u8				cb;
> +	u32				nburst;
> +	struct dw_edma_burst            burst[] __counted_by(nburst);
>  };
>  
>  struct dw_edma_chan {
> @@ -126,7 +125,6 @@ struct dw_edma_core_ops {
>  	void (*ll_link)(struct dw_edma_chan *chan, u32 idx, bool cb, u64 addr);
>  	void (*ch_doorbell)(struct dw_edma_chan *chan);
>  	void (*ch_enable)(struct dw_edma_chan *chan);
> -
>  	void (*ch_config)(struct dw_edma_chan *chan);
>  	void (*debugfs_on)(struct dw_edma *dw);
>  };
> @@ -166,6 +164,14 @@ struct dw_edma_chan *dchan2dw_edma_chan(struct dma_chan *dchan)
>  	return vc2dw_edma_chan(to_virt_chan(dchan));
>  }
>  
> +static inline u64 dw_edma_core_get_ll_paddr(struct dw_edma_chan *chan)

No need of inline.

- Mani

-- 
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