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From: Mark Brown <broonie@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	linux-kernel@vger.kernel.org,
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
	<linux-arm-kernel@lists.infradead.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	Scott Branden <sbranden@broadcom.com>,
	lukas@wunner.de, Ray Jui <rjui@broadcom.com>,
	Rob Herring <robh+dt@kernel.org>,
	"open list:SPI SUBSYSTEM" <linux-spi@vger.kernel.org>,
	"maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." 
	<bcm-kernel-feedback-list@broadcom.com>,
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
	<linux-rpi-kernel@lists.infradead.org>,
	Martin Sperl <kernel@martin.sperl.org>,
	Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support
Date: Fri, 5 Jun 2020 14:20:37 +0100	[thread overview]
Message-ID: <20200605132037.GF5413@sirena.org.uk> (raw)
In-Reply-To: <142d48ae-2725-1368-3e11-658449662371@arm.com>

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On Fri, Jun 05, 2020 at 12:34:36PM +0100, Robin Murphy wrote:
> On 2020-06-04 22:28, Florian Fainelli wrote:

> > For the BCM2835 case which is deemed performance critical, we would like
> > to continue using an interrupt handler which does not have the extra
> > comparison on BCM2835_SPI_CS_INTR.

> FWIW, if I'm reading the patch correctly, then with sensible codegen that
> "overhead" should amount to a bit test on a live register plus a not-taken
> conditional branch - according to the 1176 TRM that should add up to a
> whopping 2 cycles. If that's really significant then I'd have to wonder
> whether you want to be at the mercy of the whole generic IRQ stack at all,
> and should perhaps consider using FIQ instead.

Yes, and indeed the compiler does seem to manage that.  It *is* non-zero
overhead though.

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  reply	other threads:[~2020-06-05 13:20 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-04 21:28 Florian Fainelli
2020-06-05  8:46 ` Nicolas Saenz Julienne
2020-06-05 10:52   ` Mark Brown
2020-06-05 10:58   ` Nicolas Saenz Julienne
2020-06-05 10:51 ` Lukas Wunner
2020-06-05 11:14 ` Mark Brown
2020-06-05 12:20   ` Mark Brown
2020-06-05 11:34 ` Robin Murphy
2020-06-05 13:20   ` Mark Brown [this message]
2020-06-05 13:46     ` Robin Murphy
2020-06-05 14:41       ` Robin Murphy
2020-06-05 15:27         ` Mark Brown
2020-06-05 22:04         ` Florian Fainelli
2020-06-08 11:11           ` Robin Murphy
2020-06-08 11:28             ` Mark Brown
2020-06-15 16:34               ` Florian Fainelli
2020-06-15 17:00                 ` Mark Brown
2020-06-15 17:04                   ` Florian Fainelli
2020-06-15 17:30                     ` Mark Brown
2020-06-15 17:31                     ` Robin Murphy
2020-06-15 19:26                       ` Mark Brown
2020-06-08 11:41             ` Lukas Wunner
2020-06-15 19:09               ` Robin Murphy
2020-06-15 19:42                 ` Florian Fainelli
2020-06-15 20:48                   ` Mark Brown

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