linux-kernel - Re: [PATCH 1/4] spi: Add option to wake a device by toggling CS

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Message-ID: <20160702014551.GB27937@apronin0.mtv.corp.google.com>
Date:	Fri, 1 Jul 2016 18:45:52 -0700
From:	Andrey Pronin <apronin@...omium.org>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH 1/4] spi: Add option to wake a device by toggling CS

On Fri, Jul 01, 2016 at 09:02:30AM +0100, Mark Brown wrote:
> On Wed, Jun 29, 2016 at 08:54:24PM -0700, apronin@...omium.org wrote:
> > From: Andrey Pronin <apronin@...omium.org>
> > 
> > Some SPI devices may go to sleep after a period of inactivity
> > on SPI. For such devices, if enough time has passed since the
> > last SPI transaction, toggle CS and wait for the device to
> > start before communicating with it.
> 
> This seems incredibly specialist, I can imagine someone might implement
> something like this but it really feels like something I'd expect the
> driver for the device to be doing rather than the core.  Is it really a
> bounce that's needed and not something like putting a small delay after
> asserting chip select?

Yes, I agree it's quite device-specific, though, I guess, more than a
single device can benefit from that. I'm playing with it now to see if
I can indeed move it to a more device-specific driver from generic spi.

It is indeed a bounce and a rather long delay to let the device actually
wake from a long sleep, go through internal startup, test, etc.