Re: should we have a Kconfig "device group" for I2C devices?

[Paolo Bonzini <pbonzini@redhat.com>]

On 1/28/22 15:17, Peter Maydell wrote:
> Hi; I've been looking into what is the right way to handle in Kconfig
> an i2c device which is intended for the user to specify on the command
> line with a -device option.
> (It's the lsm303dlhc magnetometer, currently in code review:
> https://patchew.org/QEMU/20210921093227.18592-1-kevin.townsend@linaro.org/  )
> 
> Currently all our i2c devices are just pulled in by "select FOO" from
> the Kconfig stanza for a board which has that kind of sensor hardwired
> on-board. But for at least some of them it works fine to just specify
> them on the commandline of any board that has an i2c controller that
> allows pluggable devices. (For instance we do that kind of commandline
> plugging in our test suite with tests/qtest/tmp105-test.c.)
> 
> What's the best way to structure this? For PCI we have the "device
> group" PCI_DEVICES as documented in
> https://qemu-project.gitlab.io/qemu/devel/kconfig.html#guidelines-for-writing-kconfig-files
> and PCI devices say
>      default y if PCI_DEVICES
>      depends on PCI
> 
> For ISA devices we seem to make them say
>      default y
>      depends on ISA_BUS
> 
> I2C devices currently just say
>      depends on I2C
> 
> Should we have an I2C_DEVICES, which boards where there's a sensible
> user-pluggable i2c controller can specifically select ? Or should we
> mark the i2c devices which are sensibly user-pluggable as
> "default y" ? Or something else ?

Yes, I think it's a good idea to have I2C_DEVICES like we have 
PCI_DEVICES.  This way we can skip them on x86 (where the SMBus 
controller is mostly a legacy device) but include them by default on 
AVR, embedded ARM, etc.

Paolo