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

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Message-ID: <20160702020216.GA31918@apronin0.mtv.corp.google.com>
Date:	Fri, 1 Jul 2016 19:02:17 -0700
From:	Andrey Pronin <apronin@...omium.org>
To:	Mark Brown <broonie@...nel.org>
Cc:	Doug Anderson <dianders@...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 07:17:08PM +0200, Mark Brown wrote:
> 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.

Lots of godd points in the feedback. Let me re-visit the whole idea.
And may be I'll move it to a more device-specific driver.