Re: [PATCH v8 7/8] dmaengine: sh: rz-dmac: Add device_tx_status() callback

[Frank Li]

On Tue, Jan 20, 2026 at 03:33:29PM +0200, Claudiu wrote:
> From: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
>
> Add support for device_tx_status() callback as it is needed for
> RZ/G2L SCIFA driver.
>
> Based on a patch in the BSP similar to rcar-dmac by
> Long Luu <long.luu.ur@xxxxxxxxxxx>.

If you want to give credit to Long Luu, any public link?

>
> Signed-off-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx>
> [claudiu.beznea:
>  - post-increment lmdesc in rz_dmac_get_next_lmdesc() to allow the next
>    pointer to advance
>  - use 'lmdesc->nxla != crla' comparison instead of
>    '!(lmdesc->nxla == crla)' in rz_dmac_calculate_residue_bytes_in_vd()
>  - in rz_dmac_calculate_residue_bytes_in_vd() use '++i >= DMAC_NR_LMDESC'
>    to verify if the full lmdesc list was checked
>  - drop rz_dmac_calculate_total_bytes_in_vd() and use desc->len instead
>  - re-arranged comments so they span fewer lines and are wrapped to ~80
>    characters
>  - use u32 for the residue value and the functions returning it
>  - use u32 for the variables storing register values
>  - fixed typos]

Suppose needn't this section

> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@xxxxxxxxxxxxxx>
> ---
>
> Changes in v8:
> - populated engine->residue_granularity
>
> Changes in v7:
> - none
>
> Changes in v6:
> - s/byte/bytes in comment from rz_dmac_chan_get_residue()
>
> Changes in v5:
> - post-increment lmdesc in rz_dmac_get_next_lmdesc() to allow the next
>   pointer to advance
> - use 'lmdesc->nxla != crla' comparison instead of
>   '!(lmdesc->nxla == crla)' in rz_dmac_calculate_residue_bytes_in_vd()
> - in rz_dmac_calculate_residue_bytes_in_vd() use '++i >= DMAC_NR_LMDESC'
>   to verify if the full lmdesc list was checked
> - drop rz_dmac_calculate_total_bytes_in_vd() and use desc->len instead
> - re-arranged comments so they span fewer lines and are wrapped to ~80
>   characters
> - use u32 for the residue value and the functions returning it
> - use u32 for the variables storing register values
> - fixed typos
>
>  drivers/dma/sh/rz-dmac.c | 145 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 144 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/sh/rz-dmac.c b/drivers/dma/sh/rz-dmac.c
> index 4602f8b7408a..27c963083e29 100644
> --- a/drivers/dma/sh/rz-dmac.c
> +++ b/drivers/dma/sh/rz-dmac.c
> @@ -125,10 +125,12 @@ struct rz_dmac {
>   * Registers
>   */
>
> +#define CRTB				0x0020
>  #define CHSTAT				0x0024
>  #define CHCTRL				0x0028
>  #define CHCFG				0x002c
>  #define NXLA				0x0038
> +#define CRLA				0x003c
>
>  #define DCTRL				0x0000
>
> @@ -684,6 +686,146 @@ static void rz_dmac_device_synchronize(struct dma_chan *chan)
>  	rz_dmac_set_dma_req_no(dmac, channel->index, dmac->info->default_dma_req_no);
>  }
>
> +static struct rz_lmdesc *
> +rz_dmac_get_next_lmdesc(struct rz_lmdesc *base, struct rz_lmdesc *lmdesc)
> +{
> +	struct rz_lmdesc *next = ++lmdesc;
> +
> +	if (next >= base + DMAC_NR_LMDESC)
> +		next = base;
> +
> +	return next;
> +}
> +
> +static u32 rz_dmac_calculate_residue_bytes_in_vd(struct rz_dmac_chan *channel)
> +{
> +	struct rz_lmdesc *lmdesc = channel->lmdesc.head;
> +	struct dma_chan *chan = &channel->vc.chan;
> +	struct rz_dmac *dmac = to_rz_dmac(chan->device);
> +	u32 residue = 0, crla, i = 0;
> +
> +	crla = rz_dmac_ch_readl(channel, CRLA, 1);
> +	while (lmdesc->nxla != crla) {
> +		lmdesc = rz_dmac_get_next_lmdesc(channel->lmdesc.base, lmdesc);
> +		if (++i >= DMAC_NR_LMDESC)
> +			return 0;
> +	}
> +
> +	/* Calculate residue from next lmdesc to end of virtual desc */
> +	while (lmdesc->chcfg & CHCFG_DEM) {
> +		residue += lmdesc->tb;
> +		lmdesc = rz_dmac_get_next_lmdesc(channel->lmdesc.base, lmdesc);
> +	}

can use one loop

for (int i=0; i<DMAC_NR_LMDESC; i++) {
	if (lmdesc->nxla == crla)
		residue = 0; 	//reset to 0;

	if (lmdesc->chcfg & CHCFG_DEM)
		residue += lmdesc->tb;

	lmdesc = rz_dmac_get_next_lmdesc(channel->lmdesc.base, lmdesc);
}

return residue;

> +
> +	dev_dbg(dmac->dev, "%s: VD residue is %u\n", __func__, residue);
> +
> +	return residue;
> +}
> +
> +static u32 rz_dmac_chan_get_residue(struct rz_dmac_chan *channel,
> +				    dma_cookie_t cookie)
> +{
> +	struct rz_dmac_desc *current_desc, *desc;
> +	enum dma_status status;
> +	u32 crla, crtb, i;
> +
> +	/* Get current processing virtual descriptor */
> +	current_desc = list_first_entry(&channel->ld_active,
> +					struct rz_dmac_desc, node);
> +	if (!current_desc)
> +		return 0;
> +
> +	/*
> +	 * If the cookie corresponds to a descriptor that has been completed
> +	 * there is no residue. The same check has already been performed by the
> +	 * caller but without holding the channel lock, so the descriptor could
> +	 * now be complete.
> +	 */
> +	status = dma_cookie_status(&channel->vc.chan, cookie, NULL);
> +	if (status == DMA_COMPLETE)
> +		return 0;
> +
> +	/*
> +	 * If the cookie doesn't correspond to the currently processing virtual
> +	 * descriptor then the descriptor hasn't been processed yet, and the
> +	 * residue is equal to the full descriptor size. Also, a client driver
> +	 * is possible to call this function before rz_dmac_irq_handler_thread()
> +	 * runs. In this case, the running descriptor will be the next
> +	 * descriptor, and will appear in the done list. So, if the argument
> +	 * cookie matches the done list's cookie, we can assume the residue is
> +	 * zero.
> +	 */
> +	if (cookie != current_desc->vd.tx.cookie) {
> +		list_for_each_entry(desc, &channel->ld_free, node) {
> +			if (cookie == desc->vd.tx.cookie)
> +				return 0;
> +		}
> +
> +		list_for_each_entry(desc, &channel->ld_queue, node) {
> +			if (cookie == desc->vd.tx.cookie)
> +				return desc->len;
> +		}
> +
> +		list_for_each_entry(desc, &channel->ld_active, node) {
> +			if (cookie == desc->vd.tx.cookie)
> +				return desc->len;
> +		}
> +
> +		/*
> +		 * No descriptor found for the cookie, there's thus no residue.
> +		 * This shouldn't happen if the calling driver passes a correct
> +		 * cookie value.
> +		 */
> +		WARN(1, "No descriptor for cookie!");
> +		return 0;
> +	}
> +
> +	/*
> +	 * We need to read two registers. Make sure the hardware does not move
> +	 * to next lmdesc while reading the current lmdesc. Trying it 3 times
> +	 * should be enough: initial read, retry, retry for the paranoid.
> +	 */
> +	for (i = 0; i < 3; i++) {
> +		crla = rz_dmac_ch_readl(channel, CRLA, 1);
> +		crtb = rz_dmac_ch_readl(channel, CRTB, 1);
> +		/* Still the same? */
> +		if (crla == rz_dmac_ch_readl(channel, CRLA, 1))
> +			break;
> +	}
> +
> +	WARN_ONCE(i >= 3, "residue might not be continuous!");
> +
> +	/*
> +	 * Calculate number of bytes transferred in processing virtual descriptor.
> +	 * One virtual descriptor can have many lmdesc.
> +	 */
> +	return crtb + rz_dmac_calculate_residue_bytes_in_vd(channel);

you don't use varible 'ctra' here, so retry 3 become useless. suppose
rz_dmac_calculate_residue_bytes_in_vd(channel, ctra)

and avoid rz_dmac_ch_readl(channel, CRLA, 1) in
rz_dmac_calculate_residue_bytes_in_vd() to keep ctra and ctrb reflect the
correct hardware state.

Frank

> +}
> +
> +static enum dma_status rz_dmac_tx_status(struct dma_chan *chan,
> +					 dma_cookie_t cookie,
> +					 struct dma_tx_state *txstate)
> +{
> +	struct rz_dmac_chan *channel = to_rz_dmac_chan(chan);
> +	enum dma_status status;
> +	u32 residue;
> +
> +	status = dma_cookie_status(chan, cookie, txstate);
> +	if (status == DMA_COMPLETE || !txstate)
> +		return status;
> +
> +	scoped_guard(spinlock_irqsave, &channel->vc.lock)
> +		residue = rz_dmac_chan_get_residue(channel, cookie);
> +
> +	/* if there's no residue, the cookie is complete */
> +	if (!residue)
> +		return DMA_COMPLETE;
> +
> +	dma_set_residue(txstate, residue);
> +
> +	return status;
> +}
> +
>  /*
>   * -----------------------------------------------------------------------------
>   * IRQ handling
> @@ -1007,6 +1149,7 @@ static int rz_dmac_probe(struct platform_device *pdev)
>  	engine = &dmac->engine;
>  	dma_cap_set(DMA_SLAVE, engine->cap_mask);
>  	dma_cap_set(DMA_MEMCPY, engine->cap_mask);
> +	engine->residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
>  	rz_dmac_writel(dmac, DCTRL_DEFAULT, CHANNEL_0_7_COMMON_BASE + DCTRL);
>  	rz_dmac_writel(dmac, DCTRL_DEFAULT, CHANNEL_8_15_COMMON_BASE + DCTRL);
>
> @@ -1014,7 +1157,7 @@ static int rz_dmac_probe(struct platform_device *pdev)
>
>  	engine->device_alloc_chan_resources = rz_dmac_alloc_chan_resources;
>  	engine->device_free_chan_resources = rz_dmac_free_chan_resources;
> -	engine->device_tx_status = dma_cookie_status;
> +	engine->device_tx_status = rz_dmac_tx_status;
>  	engine->device_prep_slave_sg = rz_dmac_prep_slave_sg;
>  	engine->device_prep_dma_memcpy = rz_dmac_prep_dma_memcpy;
>  	engine->device_config = rz_dmac_config;
> --
> 2.43.0
>