Re: [PATCH v2 23/23] dmaengine: sdxi: Add DMA engine provider

[Frank Li]

On Mon, May 11, 2026 at 05:28:01PM -0500, Lynch, Nathan wrote:
> On 5/11/2026 3:47 PM, Frank Li wrote:
> >> +static struct dma_async_tx_descriptor *
> >> +sdxi_dma_prep_memcpy(struct dma_chan *dma_chan, dma_addr_t dst,
> >> +		     dma_addr_t src, size_t len, unsigned long flags)
> >> +{
> >> +	struct sdxi_akey_ent *akey = to_sdxi_dma_chan(dma_chan)->akey;
> >> +	struct sdxi_cxt *cxt = to_sdxi_dma_chan(dma_chan)->cxt;
> >> +	u16 akey_index = sdxi_akey_index(cxt, akey);
> >> +	struct sdxi_dma_desc *sddesc;
> >> +	struct sdxi_copy copy = {
> >> +		.src = src,
> >> +		.dst = dst,
> >> +		.src_akey = akey_index,
> >> +		.dst_akey = akey_index,
> >> +		.len = len,
> >> +	};
> >> +
> >> +	/*
> >> +	 * Perform a trial encode to a dummy descriptor on the stack
> >> +	 * so we can reject bad inputs without touching the ring
> >> +	 * state.
> >> +	 */
> >> +	if (sdxi_encode_copy(&(struct sdxi_desc){}, &copy))
> >> +		return NULL;
> >> +
> >> +	sddesc = (flags & DMA_PREP_INTERRUPT) ?
> >> +		prep_memcpy_intr(dma_chan, &copy) :
> >> +		prep_memcpy_polled(dma_chan, &copy);
> >
> > Maybe I am wrong. According to my understand "DMA_PREP_INTERRUPT" is trigger
> > irq when complete.  without DMA_PREP_INTERRUPT, don't trigger irq when
> > complete, not means use polling.
>
> OK, my choice of function names there arises from the dmatest 'polled'
> parameter which selects the completion signaling mode. I can rename it
> to prep_memcpy_nointr() or otherwise refactor to avoid the confusion, if
> that's the issue.

suppose only one line difference between prep_memcpy_intr() and prep_memcpy_polled()

prep_memcpy(dma_chan, &copy, flags)
{
	...
	if (flags & DMA_PREP_INTERRUPT)
		... enable_irq
	else
		... disable_irq
}

of cause prep_memcpy_nointr() also okay.

Frank

>
>
> > for example,
> > tx1 = prep(flags = 0)
> > submit(tx1);
> > tx2 = prep(flags = DMA_PREP_INTERRUPT)
> > submit(tx2);
> >
> > issue_pending();
> >
> > DMA Consummer just expect get irq when tx2 complete to reduce irq numbers.
>
> Yes, I believe the SDXI DMA provider satisfies this expectation as
> currently written.
>
> > If using polling here, it will reduce transfer efficacy.
>
> The SDXI code does not poll for any descriptor's status unless the
> dmaengine API asks it to, I think? E.g. via device_tx_status().