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From:   Ikjoon Jang <ikjn@chromium.org>
Date:   Tue, 2 Mar 2021 19:30:21 +0800
Message-ID: <CAATdQgCoLB-iOcxN2ptDmqD69FnyUen5XeRTq=LCCfXmWkBeWw@mail.gmail.com>
Subject: Re: [PATCH] i2c: mediatek: Get device clock-stretch time via dts
To:     qii.wang@mediatek.com
Cc:     wsa@the-dreams.de, srv_heupstream <srv_heupstream@mediatek.com>,
        leilk.liu@mediatek.com, open list <linux-kernel@vger.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>, linux-i2c@vger.kernel.org,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@lists.infradead.org>
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Hi Qii,

On Wed, Feb 3, 2021 at 6:43 PM <qii.wang@mediatek.com> wrote:
>
> From: Qii Wang <qii.wang@mediatek.com>
>
> tSU,STA/tHD,STA/tSU,STOP maybe out of spec due to device
> clock-stretching or circuit loss, we could get device
> clock-stretch time from dts to adjust these parameters
> to meet the spec via EXT_CONF register.
>
> Signed-off-by: Qii Wang <qii.wang@mediatek.com>
> ---
>  drivers/i2c/busses/i2c-mt65xx.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
> index 2ffd2f3..47c7255 100644
> --- a/drivers/i2c/busses/i2c-mt65xx.c
> +++ b/drivers/i2c/busses/i2c-mt65xx.c
> @@ -245,6 +245,7 @@ struct mtk_i2c {
>         u16 irq_stat;                   /* interrupt status */
>         unsigned int clk_src_div;
>         unsigned int speed_hz;          /* The speed in transfer */
> +       unsigned int clock_stretch_ns;
>         enum mtk_trans_op op;
>         u16 timing_reg;
>         u16 high_speed_reg;
> @@ -607,7 +608,8 @@ static int mtk_i2c_check_ac_timing(struct mtk_i2c *i2c,
>         else
>                 clk_ns = sample_ns / 2;
>
> -       su_sta_cnt = DIV_ROUND_UP(spec->min_su_sta_ns, clk_ns);
> +       su_sta_cnt = DIV_ROUND_UP(spec->min_su_sta_ns + i2c->clock_stretch_ns,
> +                                 clk_ns);
>         if (su_sta_cnt > max_sta_cnt)
>                 return -1;
>
> @@ -1171,6 +1173,8 @@ static int mtk_i2c_parse_dt(struct device_node *np, struct mtk_i2c *i2c)
>         if (i2c->clk_src_div == 0)
>                 return -EINVAL;
>
> +       of_property_read_u32(np, "clock-stretch-ns", &i2c->clock_stretch_ns);
> +

I think this new property "clock-stretch-ns" is for the same purpose of
"i2c-scl-falling-time-ns" + "i2c-scl-rising-time-ns" defined in
Documentation/devicetree/bindings/i2c/i2c.txt?

>         i2c->have_pmic = of_property_read_bool(np, "mediatek,have-pmic");
>         i2c->use_push_pull =
>                 of_property_read_bool(np, "mediatek,use-push-pull");
> --
> 1.9.1
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