linux-kernel - Re: [PATCH v2 08/11] spi: cadence-qspi: add early busywait to cqspi_wait_for

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Date: Mon, 8 Apr 2024 17:40:32 +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 08/11] spi: cadence-qspi: add early busywait to
 cqspi_wait_for_bit()

On Mon, Apr 08, 2024 at 04:42:43PM +0200, Théo Lebrun wrote:
> On Mon Apr 8, 2024 at 4:16 PM CEST, Mark Brown wrote:
> > On Fri, Apr 05, 2024 at 05:02:18PM +0200, Théo Lebrun wrote:

> > > The reason is to avoid hrtimer interrupts on the system. All read
> > > operations take less than 100µs.

> > Why would this be platform specific, this seems like a very standard
> > optimisation technique?

> It does not make sense if you know that all read operations take more
> than 100µs. I preferred being conservative. If you confirm it makes
> sense I'll remove the quirk.

It does seem plausible at least, and the time could be made a tuneable
with quirks or otherwise if that's needed.  I think I'd expect the MIPS
platform you're working with to be towards the lower end of performance
for systems that are new enough to have this hardware.

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