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

Claudiu Beznea
2026-04-11T12:38:44Z

On 4/11/26 15:34, Biju Das wrote:
> Hi Claudiu,
>
>> -----Original Message-----
>> From: Claudiu <claudiu.beznea@tuxon.dev>
>> 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@bp.renesas.com>
>>
>> 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@bp.renesas.com>
>> ---
>>
>> 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