linux-kernel - Re: [PATCH v1 1/2] i2c:busses:Register PCI1XXXX adapter to I2C subsystem

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Date:   Thu, 7 Oct 2021 19:33:18 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     LakshmiPraveen Kopparthi <LakshmiPraveen.Kopparthi@...rochip.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Wolfram Sang <wsa@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        s.shtylyov@....ru, linux-i2c <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/2] i2c:busses:Register PCI1XXXX adapter to I2C subsystem

On Thu, Oct 7, 2021 at 7:25 PM Dmitry Osipenko <digetx@...il.com> wrote:
> 05.10.2021 11:50, LakshmiPraveen Kopparthi пишет:
> >> Why i2c->freq is fixed to I2C_MAX_FAST_MODE_FREQ in
> >> pci1xxxx_i2c_init()?
> > This is the default frequency at which the adapter shall operate. This
> > driver is targeted for x86,X64 platforms. Could you please suggest a
> > way to configure the freqeuncy?
>
> For x86 it should come somewhere from ACPI info presumably, but I'm not
> ACPI expert. Andy may have more insight.
>
> At least you could add a clarifying comment to the code, telling why
> freq is fixed to the standard speed.

Since it's a host controller adapter driver we have to choose
something it will operate by default. In ACPI the peripheral may ask
for higher or lower speed and in i2c_acpi_find_bus_speed() [1] we
decide at which speed it should be.

[1]: https://elixir.bootlin.com/linux/latest/source/drivers/i2c/i2c-core-acpi.c#L331

-- 
With Best Regards,
Andy Shevchenko