linux-kernel - Re: [PATCH] i2c: rk3x: Account for repeated start time requirement

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Message-ID: <CAD=FV=VT_vzn_7EPfokA50B42ObDuXdtWEu72Dq6DHXt0QXFzA@mail.gmail.com>
Date:	Thu, 11 Dec 2014 13:58:20 -0800
From:	Doug Anderson <dianders@...omium.org>
To:	Wolfram Sang <wsa@...-dreams.de>,
	Max Schwarz <max.schwarz@...ine.de>
Cc:	Heiko Stübner <heiko@...ech.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Addy Ke <addy.ke@...k-chips.com>,
	Lin Huang <hl@...k-chips.com>, yiwei cai <cyw@...k-chips.com>,
	Doug Anderson <dianders@...omium.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: Re: [PATCH] i2c: rk3x: Account for repeated start time requirement

Hi,

On Thu, Dec 11, 2014 at 11:18 AM, Doug Anderson <dianders@...omium.org> wrote:
> -       min_low_ns = spec_min_low_ns + fall_ns;
> -       min_high_ns = spec_min_high_ns + rise_ns;
> +       /*
> +        * For repeated start we need at least (spec_setup_start * 2) to meet
> +        * (tSU;SDA) requirements. The controller drops data low at half the
> +        * high time). Also need to meet normal specification requirements.
> +        */
> +       if (for_start)
> +               min_high_ns = max(spec_setup_start * 2,
> +                                 spec_setup_start + sda_fall_ns +
> +                                 spec_min_high_ns);
> +       else
> +               min_high_ns = spec_min_high_ns;
> +       min_high_ns += scl_rise_ns;
> +
> +       min_low_ns = spec_min_low_ns + scl_fall_ns;

Sorry I didn't think about this before, but I think the above has a
slight bug.  I need to account for the scl_rise_ns rise time twice in
the repeated start case, I believe.  I'll send out a new version
shortly.
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