Re: [PATCH 2/2] dmaengine: Add Arm DMA-350 driver

[Vinod Koul <vkoul@kernel.org>]

On 11-03-25, 12:48, Robin Murphy wrote:
> On 2025-03-10 8:47 pm, Vinod Koul wrote:
> > On 28-02-25, 17:26, Robin Murphy wrote:
> > 
> > > +static u32 d350_get_residue(struct d350_chan *dch)
> > > +{
> > > +	u32 res, xsize, xsizehi, hi_new;
> > > +
> > > +	hi_new = readl_relaxed(dch->base + CH_XSIZEHI);
> > > +	do {
> > > +		xsizehi = hi_new;
> > > +		xsize = readl_relaxed(dch->base + CH_XSIZE);
> > > +		hi_new = readl_relaxed(dch->base + CH_XSIZEHI);
> > > +	} while (xsizehi != hi_new);
> > 
> > This can go forever, lets have some limits to this loop please
> 
> Sure, in practice I doubt we're ever going to be continually preempted
> faster than the controller can move another 64KB of data, but I concur
> there's no harm in making the code easier to reason about at a glance
> either.

Yes you are coreect but when things go bad, a bug in h/w or something, I
would like to see a fail safe

> > > +static int d350_alloc_chan_resources(struct dma_chan *chan)
> > > +{
> > > +	struct d350_chan *dch = to_d350_chan(chan);
> > > +	int ret = request_irq(dch->irq, d350_irq, IRQF_SHARED,
> > > +			      dev_name(&dch->vc.chan.dev->device), dch);
> > 
> > This is interesting, any reason why the irq is allocated here? Would it
> > be not better to do that in probe...
> 
> Well, I'd say technically the IRQ is a channel resource, and quite a few
> other drivers do the same... Here it's mostly so I can get the channel name
> - so the IRQs are nice and identifiable in /proc/interrupts - easily without
> making a big mess in probe, since the names don't exist until after the
> device is registered.

Ok

-- 
~Vinod