linux-kernel - Re: [PATCH v7 9/9] i2c: rk3x: support fast-mode plus for rk3399

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Date:	Thu, 5 May 2016 16:02:16 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	David Wu <david.wu@...k-chips.com>
Cc:	Heiko Stübner <heiko@...ech.de>,
	Wolfram Sang <wsa@...-dreams.de>,
	Rob Herring <robh+dt@...nel.org>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Brian Norris <briannorris@...gle.com>,
	David Riley <davidriley@...gle.com>,
	Tao Huang <huangtao@...k-chips.com>,
	Lin Huang <hl@...k-chips.com>, Jianqun Xu <xjq@...k-chips.com>,
	Chris <zyw@...k-chips.com>, Eddie Cai <cf@...k-chips.com>,
	"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>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 9/9] i2c: rk3x: support fast-mode plus for rk3399

David,

On Wed, May 4, 2016 at 7:37 AM, David Wu <david.wu@...k-chips.com> wrote:
> Signed-off-by: David Wu <david.wu@...k-chips.com>
> ---
>  drivers/i2c/busses/i2c-rk3x.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-rk3x.c b/drivers/i2c/busses/i2c-rk3x.c
> index 47368c4..c66cc39 100644
> --- a/drivers/i2c/busses/i2c-rk3x.c
> +++ b/drivers/i2c/busses/i2c-rk3x.c
> @@ -124,6 +124,17 @@ static const struct i2c_spec_values fast_mode_spec = {
>         .min_hold_buffer_ns = 1300,
>  };
>
> +static const struct i2c_spec_values fast_mode_plus_spec = {
> +       .min_hold_start_ns = 260,
> +       .min_low_ns = 500,
> +       .min_high_ns = 260,
> +       .min_setup_start_ns = 260,
> +       .max_data_hold_ns = 400,

I'm curious where you got the data_hold_ns.  I can't quite remember
what this parameter does / how the timing function works anymore, but
the doc I have (search for UM10204 and click the first link) shows
values for Standard-mode and Fast-mode but not Fast-mode Plus.  It
seems to imply that this is a bit of a bogus number anyway because it
only matters if we don't stretch the tLOW to go along with the longer
data hold.

As I have said in the previous patch, how all this stuff works has
totally left my brain, so if you understand it that's probably good
enough.  If you feel like I should try to re-understand this again so
I can review it more deeply, let me know.


Since I assume that you had some sane reason to include max_data_hold_ns:

Reviewed-by: Douglas Anderson <dianders@...omium.org>