linux-kernel - Re: [PATCH v2 05/11] spi: cadence-qspi: add FIFO depth detection quirk

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Message-ID: <66bf7d58-a726-49ba-9765-f769f6189310@sirena.org.uk>
Date: Mon, 8 Apr 2024 15:51:26 +0100
From: Mark Brown <broonie@...nel.org>
To: Théo Lebrun <theo.lebrun@...tlin.com>
Cc: Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Vaishnav Achath <vaishnav.a@...com>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Rob Herring <robh@...nel.org>, linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mips@...r.kernel.org,
	Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>,
	Gregory CLEMENT <gregory.clement@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	Tawfik Bayouk <tawfik.bayouk@...ileye.com>
Subject: Re: [PATCH v2 05/11] spi: cadence-qspi: add FIFO depth detection
 quirk

On Mon, Apr 08, 2024 at 04:38:56PM +0200, Théo Lebrun wrote:
> On Mon Apr 8, 2024 at 4:10 PM CEST, Mark Brown wrote:
> > On Fri, Apr 05, 2024 at 05:02:15PM +0200, Théo Lebrun wrote:

> > > +	if (ddata && ddata->quirks & CQSPI_DETECT_FIFO_DEPTH) {
> > > +		cqspi->fifo_depth = fifo_depth;
> > > +		dev_dbg(dev, "using FIFO depth of %u\n", fifo_depth);
> > > +	} else if (fifo_depth != cqspi->fifo_depth) {
> > > +		dev_warn(dev, "detected FIFO depth (%u) different from config (%u)\n",
> > > +			 fifo_depth, cqspi->fifo_depth);
> > > +	}

> > It's not obvious to me that we should ignore an explicitly specified
> > property if the quirk is present

> DT value isn't expected for compatibles with CQSPI_DETECT_FIFO_DEPTH
> quirk, therefore we do not ignore a specified property. Bindings agree:
> prop is false with EyeQ5 compatible.

Sure, but it's not obvious that that is the most helpful or constructive
way to handle things.

> > - if anything I'd more expect to see
> > the new warning in that case, possibly with a higher severity if we're
> > saying that the quirk means we're more confident that the data reported
> > by the hardware is reliable.  I think what I'd expect is that we always
> > use an explicitly specified depth (hopefully the user was specifying it
> > for a reason?).

> The goal was a simpler devicetree on Mobileye platform. This is why we
> add this behavior flag. You prefer the property to be always present?
> This is a only a nice-to-have, you tell me what you prefer.

I would prefer that the property is always optional, or only required on
platforms where we know that the depth isn't probeable.

> I wasn't sure all HW behaved in the same way wrt read-only bits in
> SRAMPARTITION, and I do not have access to other platforms exploiting
> this driver. This is why I kept behavior reserved for EyeQ5-integrated
> IP block.

Well, if there's such little confidence that the depth is reported then
we shouldn't be logging an error.

> > Pulling all the above together can we just drop the quirk and always do
> > the detection, or leave the quirk as just controlling the severity with
> > which we log any difference between detected and explicitly configured
> > depths?

> If we do not simplify devicetree, then I'd vote for dropping this patch
> entirely. Adding code for detecting such an edge-case doesn't sound
> useful. Especially since this kind of error should only occur to people
> adding new hardware support; those probably do not need a nice
> user-facing error message. What do you think?

I'm confused why you think dropping the patch is a good idea?

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