linux-kernel - Re: [PATCH v5 2/2] iio: adc: Add the NXP SAR ADC support for the s32g2/3 platforms

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Message-ID: <aRyAuTZEi_xHkn9G@black.igk.intel.com>
Date: Tue, 18 Nov 2025 15:20:41 +0100
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: jic23@...nel.org, dlechner@...libre.com, nuno.sa@...log.com,
	robh@...nel.org, conor+dt@...nel.org, krzk+dt@...nel.org,
	linux-iio@...r.kernel.org, s32@....com,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	chester62515@...il.com, mbrugger@...e.com,
	ghennadi.procopciuc@....nxp.com
Subject: Re: [PATCH v5 2/2] iio: adc: Add the NXP SAR ADC support for the
 s32g2/3 platforms

On Fri, Nov 07, 2025 at 12:36:14PM +0100, Daniel Lezcano wrote:
> On 10/31/25 13:45, Andy Shevchenko wrote:
> > On Fri, Oct 31, 2025 at 12:32:03PM +0100, Daniel Lezcano wrote:
> > > On 10/30/25 10:28, Andy Shevchenko wrote:
> > > > On Thu, Oct 30, 2025 at 09:27:21AM +0100, Daniel Lezcano wrote:
> > > > > On 10/18/25 22:12, Andy Shevchenko wrote:
> > > > > > On Fri, Oct 17, 2025 at 06:42:38PM +0200, Daniel Lezcano wrote:

[ ... ]

> > > > > > > +	dmaengine_tx_status(info->dma_chan, info->cookie, &state);
> > > > > > 
> > > > > > No return value check?
> > > > > 
> > > > > The return value is not necessary here because the caller of the callback
> > > > > will check with dma_submit_error() in case of error which covers the
> > > > > DMA_ERROR case and the other cases are not useful because the residue is
> > > > > taken into account right after.
> > > > 
> > > > In some cases it might return DMA_PAUSE (and actually this is the correct way
> > > > to get residue, one needs to pause the channel to read it, otherwise it will
> > > > give outdated / incorrect information).
> > > 
> > > But if the residue is checked in the callback routine without checking
> > > DMA_PAUSED, the result is the same no ?
> > 
> > DMA in some corner cases might have already be charged for the next transfer.
> > Do you have a synchronisation between DMA start and residue check?
> > 
> > I.o.w. this may work for your case, but in general it's not guaranteed. The proper
> > read of residue is to: pause DMA --> read residue --> resume DMA.
> 
> I'll use the new callback function dma_async_tx_callback_result() which
> should prevent that and allows to remove the spinlock at the same time

So, AFAIU this doesn't work for you.


-- 
With Best Regards,
Andy Shevchenko