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 15:16:29 +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 Fri, Apr 05, 2024 at 05:02:18PM +0200, Théo Lebrun wrote:

> If the CQSPI_BUSYWAIT_EARLY quirk flag is on, call
> readl_relaxed_poll_timeout() with no sleep at the start of
> cqspi_wait_for_bit(). If its short timeout expires, a sleeping
> readl_relaxed_poll_timeout() call takes the relay.
> 
> Behavior is hidden behind a quirk flag to keep the previous behavior the
> same on all platforms.
> 
> 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?

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