From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wolfram Sang <wsa@the-dreams.de>
Date: Sun, 02 Nov 2014 21:53:59 +0000
Subject: Re: [RFC 0/3] i2c: sh_mobile: add DMA support
Message-Id: <20141102215359.GA1278@katana>
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List-Id: <linux-sh.vger.kernel.org>
References: <1414752678-26078-1-git-send-email-wsa@the-dreams.de>
 <21770791.t5tSlWMt1c@avalon>
In-Reply-To: <21770791.t5tSlWMt1c@avalon>
To: Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>
Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sh-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Magnus Damm <magnus.damm-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Simon Horman <horms-/R6kz+dDXgpPR4JQBCEnsQ@public.gmane.org>, Geert Uytterhoeven <geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>


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> > Here is my RFC to support DMA with the i2c-sh_mobile core. DMA works ni=
cely
> > with my tests so far and we save 1 interrupt per transferred byte, yay!
>=20
> Do we have an idea of how much power (or CPU time ?) DMA support could sa=
ve ?

I have some numbers from the function tracer, but I don't trust them.
According to them, DMA is always better (50us per interrupt vs. 23us for
DMA setup). This is why I say the threshold is still under test.


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