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

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Message-ID: <aVv57bqUAiX9Omeb@lizhi-Precision-Tower-5810>
Date: Mon, 5 Jan 2026 12:50:37 -0500
From: Frank Li <Frank.li@....com>
To: Manivannan Sadhasivam <mani@...nel.org>
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 Tue, Dec 30, 2025 at 10:31:28PM +0530, Manivannan Sadhasivam wrote:
> 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.

It is impossible that desc is NULL if vd is not NULL.

static inline
struct dw_edma_desc *vd2dw_edma_desc(struct virt_dma_desc *vd)
{
	return container_of(vd, struct dw_edma_desc, vd);
}

Previous check is reduntant.

Frank

>
> > +
> > +	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?

Sorry, forget remove it.

Frank
>
> >
> >  	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
>
> --
> மணிவண்ணன் சதாசிவம்