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From:   Stefan Binding <sbinding@opensource.cirrus.com>
To:     "'Rafael J. Wysocki'" <rafael@kernel.org>
CC:     'Mark Brown' <broonie@kernel.org>, 'Len Brown' <lenb@kernel.org>,
        'Hans de Goede' <hdegoede@redhat.com>,
        'Mark Gross' <markgross@kernel.org>,
        'Jaroslav Kysela' <perex@perex.cz>,
        'Takashi Iwai' <tiwai@suse.com>,
        "'moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM...'" 
        <alsa-devel@alsa-project.org>,
        'Linux Kernel Mailing List' <linux-kernel@vger.kernel.org>,
        'linux-spi' <linux-spi@vger.kernel.org>,
        'ACPI Devel Maling List' <linux-acpi@vger.kernel.org>,
        'Platform Driver' <platform-driver-x86@vger.kernel.org>,
        <patches@opensource.cirrus.com>
References: <20220121143254.6432-1-sbinding@opensource.cirrus.com> <20220121143254.6432-8-sbinding@opensource.cirrus.com> <CAJZ5v0gK=-SXUDekg_2DtOuMsn6Ls4gS+nymei2Qa9ZEFvqGcA@mail.gmail.com>
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Subject: RE: [PATCH v5 7/9] platform/x86: serial-multi-instantiate: Add SPI support
Date:   Fri, 21 Jan 2022 16:55:10 +0000
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Hi,

> -----Original Message-----
> From: Rafael J. Wysocki <rafael@kernel.org>
> Sent: 21 January 2022 15:31
> To: Stefan Binding <sbinding@opensource.cirrus.com>
> Cc: Mark Brown <broonie@kernel.org>; Rafael J . Wysocki
> <rafael@kernel.org>; Len Brown <lenb@kernel.org>; Hans de Goede
> <hdegoede@redhat.com>; Mark Gross <markgross@kernel.org>; Jaroslav
> Kysela <perex@perex.cz>; Takashi Iwai <tiwai@suse.com>; moderated
> list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM... <alsa-
> devel@alsa-project.org>; Linux Kernel Mailing List <linux-
> kernel@vger.kernel.org>; linux-spi <linux-spi@vger.kernel.org>; ACPI =
Devel
> Maling List <linux-acpi@vger.kernel.org>; Platform Driver =
<platform-driver-
> x86@vger.kernel.org>; patches@opensource.cirrus.com
> Subject: Re: [PATCH v5 7/9] platform/x86: serial-multi-instantiate: =
Add SPI
> support
>=20


> > diff --git a/drivers/platform/x86/Kconfig =
b/drivers/platform/x86/Kconfig
> > index 5b65d687f046..28f5bbf0f27a 100644
> > --- a/drivers/platform/x86/Kconfig
> > +++ b/drivers/platform/x86/Kconfig
> > @@ -991,12 +991,12 @@ config TOPSTAR_LAPTOP
> >           If you have a Topstar laptop, say Y or M here.
> >
> >  config SERIAL_MULTI_INSTANTIATE
> > -       tristate "I2C multi instantiate pseudo device driver"
> > -       depends on I2C && ACPI
> > +       tristate "I2C and SPI multi instantiate pseudo device =
driver"
> > +       depends on I2C && SPI && ACPI
>=20
> Should this be (I2C || SPI) && ACPI ?

We made it dependent on both I2C and SPI because of how interconnected =
the
serial-multi-instantiate driver is with both SPI and I2C. We felt =
attempting to make
the driver compatible with one without the other would end up very =
complicated.

> > @@ -146,7 +247,21 @@ static int smi_probe(struct platform_device =
*pdev)
> >
> >         platform_set_drvdata(pdev, smi);
> >
> > -       return smi_i2c_probe(pdev, adev, smi, inst_array);
> > +       switch (node->bus_type) {
> > +       case SMI_I2C:
> > +               return smi_i2c_probe(pdev, adev, smi, =
node->instances);
> > +       case SMI_SPI:
> > +               return smi_spi_probe(pdev, adev, smi, =
node->instances);
> > +       case SMI_AUTO_DETECT:
> > +               if (i2c_acpi_client_count(adev) > 0)
> > +                       return smi_i2c_probe(pdev, adev, smi, =
node->instances);
> > +               else
> > +                       return smi_spi_probe(pdev, adev, smi, =
node->instances);
> > +       default:
> > +               break;
>=20
> Why is this needed?

This return code is attempting to ensure that we don=E2=80=99t try to =
guess whether we
expect devices to be I2C or SPI - especially with regards to existing =
devices.
We wanted to maintain compatibility with existing devices, which would =
all be
I2C.
For the device for which we are adding, the same HID is used by both the =
same
chip for both I2C and SPI, so we also needed a way to support both.

Thanks,
Stefan