linux-kernel - Re: [PATCH] spi: bcm2835: Implement shutdown callback

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Message-ID: <20200529175831.p4dphb5luymgapzx@wunner.de>
Date:   Fri, 29 May 2020 19:58:31 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." 
        <bcm-kernel-feedback-list@...adcom.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        "open list:SPI SUBSYSTEM" <linux-spi@...r.kernel.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] spi: bcm2835: Implement shutdown callback

On Fri, May 29, 2020 at 10:48:11AM -0700, Florian Fainelli wrote:
> On 5/29/20 10:47 AM, Lukas Wunner wrote:
> > On Thu, May 28, 2020 at 12:06:05PM -0700, Florian Fainelli wrote:
> >> Make sure we clear the FIFOs, stop the block, disable the clock and
> >> release the DMA channel.
> > 
> > To what end?  Why is this change necessary?  Sorry but this seems like
> > an awfully terse commit message.
> 
> To ensure clocks are disabled and to save power in low power modes used
> on 7211 for instance.

Thanks for the explanation, that's an important tidbit.  I wasn't even
aware that this SPI controller is used on SoCs beyond the Raspberry Pi
ones.  Does the BCM7211 use shared interrupts for this controller?
Does it have DMA DREQ attached?