[PATCH v12 1/7] arm64: renesas: r8a7795: Add Renesas R8A7795 SoC support

[Geert Uytterhoeven]

Hi Catalin,

On Fri, Oct 30, 2015 at 12:08 PM, Catalin Marinas
<catalin.marinas at arm.com> wrote:
> On Thu, Oct 29, 2015 at 02:15:19PM +0900, Magnus Damm wrote:
>> On Thu, Oct 29, 2015 at 3:45 AM, Catalin Marinas
>> <catalin.marinas at arm.com> wrote:
>> > On Mon, Oct 26, 2015 at 03:01:46PM +0900, Simon Horman wrote:
>> >> --- a/arch/arm64/Kconfig.platforms
>> >> +++ b/arch/arm64/Kconfig.platforms
>> >> @@ -66,6 +66,23 @@ config ARCH_SEATTLE
>> >>       help
>> >>         This enables support for AMD Seattle SOC Family
>> >>
>> >> +config ARCH_SHMOBILE
>> >> +     bool
>> >> +
>> >> +config ARCH_RENESAS
>> >> +     bool "Renesas SoC Platforms"
>> >> +     select ARCH_SHMOBILE
>> >> +     select PINCTRL
>> >> +     select PM_GENERIC_DOMAINS if PM
>> >> +     help
>> >> +       This enables support for the ARMv8 based Renesas SoCs.
>> >> +
>> >> +config ARCH_R8A7795
>> >> +     bool "Renesas R-Car H3 SoC Platform"
>> >> +     depends on ARCH_RENESAS
>> >> +     help
>> >> +       This enables support for the Renesas R-Car H3 SoC.
>> >
>> > Do you need such fine-grained configuration? I'd really like to avoid
>> > individual SoC Kconfig entries and only include SoC families (like
>> > ARCH_RENESAS). There are some which I didn't spot at the time
>> > (ARCH_FSL_LS2085A and ARCH_TEGRA_132_SOC) but we shouldn't continue this
>> > trend any further.
>>
>> I agree with you about coarse grained configuration in general. I am
>> also wondering how to handle cases where IP varies with SoC version.
>> =)
>
> The code should cope with multiple drivers built into the kernel anyway,
> single Image is a hard requirement. If you want to trim down an image
> for a specific SoC (production kernel), just use individual Kconfig
> entries for drivers that may depend on ARCH_RENESAS but not an
> ARCH_R8A7795 which is used in drivers/ Makefiles.
>
>> The two most common cases with SoC-specific IP for Renesas SoCs tend
>> to be Pinctrl which is using rather large tables to support the PFC
>> hardware and also the clocks (CCF) that drives the SoC specific CPG
>> hardware. For the PFC and CPG I think it makes sense to enable build
>> based on SoC model like we do already, but for the Kconfig bits in
>> arch/arm64 perhaps ARCH_RENESAS can simply select ARCH_R8A7795?
>
> I'm suggesting the other way around: CONFIG_PINCTRL_R8A7795 which
> depends on ARCH_RENESAS, default y. Similarly for clocks and other
> drivers.

For drivers in general I agree.

Pinctrl and clocks (and perhaps a few others we haven't implemented support
for yet) are special, as they are core SoC-support: either you want all of it,
or nothing.

E.g. a kernel with CONFIG_PINCTRL_R8A7795=y but CONFIG_CLK_R8A7795=n
won't get you far.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds