linux-kernel - Re: [PATCH] spi: bcm2835: do not unregister controller in shutdown handler

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Message-ID: <20211004173531.GB3544071@ziepe.ca>
Date:   Mon, 4 Oct 2021 14:35:31 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Mark Brown <broonie@...nel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Lino Sanfilippo <LinoSanfilippo@....de>, rjui@...adcom.com,
        sbranden@...adcom.com, bcm-kernel-feedback-list@...adcom.com,
        nsaenz@...nel.org, linux-spi@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        p.rosenberger@...bus.com, linux-integrity@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] spi: bcm2835: do not unregister controller in shutdown
 handler

On Mon, Oct 04, 2021 at 06:27:29PM +0100, Mark Brown wrote:
> On Mon, Oct 04, 2021 at 02:13:01PM -0300, Jason Gunthorpe wrote:
> 
> > I'm kind of surprised a scheme like this didn't involve a FW call
> > after Linux is done with the CPUs to quiet all the HW and let it
> > sleep, I've built things that way before at least.
> 
> That's a *lot* of code to put in firmware if you can't physically power
> most of the system down.

Maybe? The chip I worked on we just made a list of register/value
pairs that covered all the functional blocks and the FW ran down the
list.

Mind you the chip was designed that poking ABC to reg 123 turned the
unit off no matter what. It didn't have a complex interactive shutdown
sequence.

Jason