linux-kernel - Re: [PATCH] spi: imx: Revert "spi: imx: enable runtime pm support"

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Message-ID: <20201012134211.GE4332@sirena.org.uk>
Date:   Mon, 12 Oct 2020 14:42:11 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     Christian Eggers <ceggers@...i.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Clark Wang <xiaoning.wang@....com>
Subject: Re: [PATCH] spi: imx: Revert "spi: imx: enable runtime pm support"

On Mon, Oct 12, 2020 at 03:28:21PM +0200, Sascha Hauer wrote:
> On Mon, Oct 12, 2020 at 12:59:34PM +0200, Christian Eggers wrote:

> > What is the benefit of controlling the SPI clock with runtime PM instead of
> > doing it manually?

> The clocks are reconfigured less frequently with pm_runtime. Especially
> when enabling/disabling PLLs are involved pm_runtime can increase
> performance.

In particular pm_runtime has support for deferring the actual disable so
if you get lots of activity in quick succession you don't actually ever
disable things until the activity stops.  This can really help reduce
overhead.

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