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From:   Stefan Binding <sbinding@opensource.cirrus.com>
To:     "'Rafael J. Wysocki'" <rafael@kernel.org>
CC:     'Platform Driver' <platform-driver-x86@vger.kernel.org>,
        "'moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM...'" 
        <alsa-devel@alsa-project.org>,
        'ACPI Devel Maling List' <linux-acpi@vger.kernel.org>,
        'Linux Kernel Mailing List' <linux-kernel@vger.kernel.org>,
        'Takashi Iwai' <tiwai@suse.com>,
        'Mark Gross' <markgross@kernel.org>,
        'Hans de Goede' <hdegoede@redhat.com>,
        'Mark Brown' <broonie@kernel.org>,
        <patches@opensource.cirrus.com>,
        'linux-spi' <linux-spi@vger.kernel.org>,
        'Len Brown' <lenb@kernel.org>
References: <20220121143254.6432-1-sbinding@opensource.cirrus.com> <20220121143254.6432-8-sbinding@opensource.cirrus.com> <CAJZ5v0gK=-SXUDekg_2DtOuMsn6Ls4gS+nymei2Qa9ZEFvqGcA@mail.gmail.com> <019901d80ee7$a6bf2a90$f43d7fb0$@opensource.cirrus.com> <CAJZ5v0j+DkX+-P1XxZ=HAnUzPjdkNFkXRTjJzhSH27KfDFAGDQ@mail.gmail.com>
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Subject: RE: [PATCH v5 7/9] platform/x86: serial-multi-instantiate: Add SPI support
Date:   Wed, 26 Jan 2022 15:19:05 +0000
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> -----Original Message-----
> From: Alsa-devel <alsa-devel-bounces@alsa-project.org> On Behalf Of
> Rafael J. Wysocki
> Sent: 21 January 2022 17:15
> To: Stefan Binding <sbinding@opensource.cirrus.com>
> Cc: Platform Driver <platform-driver-x86@vger.kernel.org>; moderated
> list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM... <alsa-
> devel@alsa-project.org>; ACPI Devel Maling List <linux-
> acpi@vger.kernel.org>; Rafael J. Wysocki <rafael@kernel.org>; Linux =
Kernel
> Mailing List <linux-kernel@vger.kernel.org>; Takashi Iwai =
<tiwai@suse.com>;
> Mark Gross <markgross@kernel.org>; Hans de Goede
> <hdegoede@redhat.com>; Mark Brown <broonie@kernel.org>;
> patches@opensource.cirrus.com; linux-spi <linux-spi@vger.kernel.org>; =
Len
> Brown <lenb@kernel.org>
> Subject: Re: [PATCH v5 7/9] platform/x86: serial-multi-instantiate: =
Add SPI
> support


>=20
> > > > @@ -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;
> > >
> > > 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.
>=20
> I meant why was the "default" case needed.  Sorry for the confusion.

I added a default case here purely for static analysis reasons. I =
don=E2=80=99t think it necessarily required, and I can remove it if =
necessary.

Thanks,
Stefan