linux-kernel - Re: [PATCH 2/2] i2c: i2c-stm32f7: allows for any bus frequency

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Message-ID: <CAHp75VdPCWdpGo=2n9g0ivti-g2m4jZ=cG4BKHBLk8BVDzaCyg@mail.gmail.com>
Date:   Wed, 25 Mar 2020 20:53:45 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Alain Volmat <alain.volmat@...com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        pierre-yves.mordret@...com,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        fabrice.gasnier@...com
Subject: Re: [PATCH 2/2] i2c: i2c-stm32f7: allows for any bus frequency

On Wed, Mar 25, 2020 at 8:38 PM Alain Volmat <alain.volmat@...com> wrote:
>
> Do not limitate to the 3 (100KHz, 400KHz, 1MHz) bus frequency but
> instead allows any frequency (if it matches timing requirements).
> Depending on the requested frequency, use the spec data from either
> Standard, Fast or Fast Plus mode.
>
> Hardcoding of min/max bus frequencies is removed and is instead computed.
>
> The driver do not use anymore speed identifier but instead handle
> directly the frequency and figure out the spec data (necessary
> for the computation of the timing register) based on the frequency.

...

> +static struct stm32f7_i2c_spec *get_specs(u32 rate)
> +{
> +       int i;
> +
> +       for (i = 0; i < ARRAY_SIZE(i2c_specs); i++)
> +               if (rate <= i2c_specs[i].rate)
> +                       return &i2c_specs[i];
> +

> +       /* NOT REACHED */
> +       return ERR_PTR(-EINVAL);

WARN_ONCE() ?

> +}

...

> -                       if ((tscl_l < i2c_specs[setup->speed].l_min) ||
> +                       if ((tscl_l < specs->l_min) ||

>                             (i2cclk >=
>                              ((tscl_l - af_delay_min - dnf_delay) / 4))) {

Perhaps squash above two to one line at the same time?

...

> +       int i;
> +
> +       for (i = ARRAY_SIZE(i2c_specs) - 1; i >= 0; i--)


Perhaps

       int i = ARRAY_SIZE(i2c_specs);

       while(i--)

?

> +               if (i2c_specs[i].rate < rate)
> +                       return i2c_specs[i].rate;

-- 
With Best Regards,
Andy Shevchenko