Re: [PATCH v4 07/17] dmaengine: sh: rz-dmac: Save the start LM descriptor

[Claudiu Beznea]

On 4/11/26 15:34, Biju Das wrote:
> Hi Claudiu,
>
> > -----Original Message-----
> > From: Claudiu <claudiu.beznea@xxxxxxxxx>
> > Sent: 11 April 2026 12:43
> > Subject: [PATCH v4 07/17] dmaengine: sh: rz-dmac: Save the start LM descriptor
> >
> > From: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> >
> > Save the start LM descriptor to avoid looping through the entire channel's LM descriptor list when
> > computing the residue. This avoids unnecessary iterations.
> >
> > Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> > ---
> >
> > Changes in v4:
> > - none
> >
> > Changes in v3:
> > - none, this patch is new
> >
> >   drivers/dma/sh/rz-dmac.c | 11 ++++++++---
> >   1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/dma/sh/rz-dmac.c b/drivers/dma/sh/rz-dmac.c index 6bea7c8c7053..0f871c0a28bd
> > 100644
> > --- a/drivers/dma/sh/rz-dmac.c
> > +++ b/drivers/dma/sh/rz-dmac.c
> > @@ -58,6 +58,7 @@ struct rz_dmac_desc {
> >   	/* For slave sg */
> >   	struct scatterlist *sg;
> >   	unsigned int sgcount;
> > +	struct rz_lmdesc *start_lmdesc;
> >   };
> >
> >   #define to_rz_dmac_desc(d)	container_of(d, struct rz_dmac_desc, vd)
> > @@ -343,6 +344,8 @@ static void rz_dmac_prepare_desc_for_memcpy(struct rz_dmac_chan *channel)
> >   	struct rz_dmac_desc *d = channel->desc;
> >   	u32 chcfg = CHCFG_MEM_COPY;
> >
> > +	d->start_lmdesc = lmdesc;
> > +
> >   	/* prepare descriptor */
> >   	lmdesc->sa = d->src;
> >   	lmdesc->da = d->dest;
> > @@ -377,6 +380,7 @@ static void rz_dmac_prepare_descs_for_slave_sg(struct rz_dmac_chan *channel)
> >   	}
> >
> >   	lmdesc = channel->lmdesc.tail;
> > +	d->start_lmdesc = lmdesc;
> >
> >   	for (i = 0, sg = sgl; i < sg_len; i++, sg = sg_next(sg)) {
> >   		if (d->direction == DMA_DEV_TO_MEM) { @@ -693,9 +697,10 @@ rz_dmac_get_next_lmdesc(struct
> > rz_lmdesc *base, struct rz_lmdesc *lmdesc)
> >   	return next;
> >   }
> >
> > -static u32 rz_dmac_calculate_residue_bytes_in_vd(struct rz_dmac_chan *channel, u32 crla)
> > +static u32 rz_dmac_calculate_residue_bytes_in_vd(struct rz_dmac_chan *channel,
> > +						 struct rz_dmac_desc *desc, u32 crla)
>
> U32 normally used with register read/writes hardware related.
>
> Here it is just computation which returns number of bytes. Unsigned int will be
> appropriate instead of u32.

Please check the type of residue as defined by dma_set_residue().

Thank you,
Claudiu