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

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Message-ID: <20160701171708.GC6247@sirena.org.uk>
Date:	Fri, 1 Jul 2016 19:17:08 +0200
From:	Mark Brown <broonie@...nel.org>
To:	Doug Anderson <dianders@...omium.org>
Cc:	apronin@...omium.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-spi <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 10:05:50AM -0700, Doug Anderson wrote:

> I'm curious why you you need a timer at all.  Can't you just keep
> track of the jiffies that you last sent and do subtraction?  ...or you
> could get even more accurate and use a ktime_t.  That avoids a whole
> lot of synchronization / locking issues too...

Yeah, that'd be a lot better.

> Also: presumably you'll need to make sure that there's some margin in
> this whole thing.  I'd imagine that if the timeout is 10000
> nanoseconds and you do the calculation and you last sent 9999
> nanoseconds ago then you might decide that the other side isn't asleep
> yet.  ...but by the time the transfer starts it might be asleep...

Indeed.

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