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Date: Mon, 8 Apr 2024 17:40:32 +0100
From: Mark Brown <broonie@kernel.org>
To: =?iso-8859-1?Q?Th=E9o?= Lebrun <theo.lebrun@bootlin.com>
Cc: Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Vaishnav Achath <vaishnav.a@ti.com>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Rob Herring <robh@kernel.org>, linux-spi@vger.kernel.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mips@vger.kernel.org,
	Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>,
	Gregory CLEMENT <gregory.clement@bootlin.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Tawfik Bayouk <tawfik.bayouk@mobileye.com>
Subject: Re: [PATCH v2 08/11] spi: cadence-qspi: add early busywait to
 cqspi_wait_for_bit()
Message-ID: <9cb48440-c71e-4a73-8104-4780f0e98e72@sirena.org.uk>
References: <20240405-cdns-qspi-mbly-v2-0-956679866d6d@bootlin.com>
 <20240405-cdns-qspi-mbly-v2-8-956679866d6d@bootlin.com>
 <1f7087ad-824e-47fe-9953-ed5152c8f18f@sirena.org.uk>
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On Mon, Apr 08, 2024 at 04:42:43PM +0200, Th=E9o 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, Th=E9o Lebrun wrote:

> > > The reason is to avoid hrtimer interrupts on the system. All read
> > > operations take less than 100=B5s.

> > 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 100=B5s. 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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