[U-Boot] [PATCH] pinctrl: renesas: Fix linker error when PINCTRL_PFC=n

[Eugeniu Rosca]

On Tue, Apr 02, 2019 at 06:02:46PM +0200, Marek Vasut wrote:
> On 4/2/19 5:40 PM, Eugeniu Rosca wrote:
> > On Tue, Apr 02, 2019 at 05:28:43PM +0200, Marek Vasut wrote:
> >> On 4/2/19 5:17 PM, Dirk Behme wrote:
> >>> On 02.04.19 15:34, Marek Vasut wrote:
> >>>> On 4/2/19 3:18 PM, Eugeniu Rosca wrote:
> >>>>> With CONFIG_PINCTRL_PFC=n, aarch64-linux-gnu-ld reports:
> >>>>>
> >>>>> -----8<-----
> >>>>>    LD      u-boot
> >>>>> drivers/gpio/built-in.o: In function `rcar_gpio_request':
> >>>>> drivers/gpio/gpio-rcar.c:128: undefined reference to
> >>>>> `sh_pfc_config_mux_for_gpio'
> >>>>> -----8<-----
[..]
> >>>> Does CONFIG_PINCTRL_PFC=n produce a bootable binary ?
> >>>
> >>> Why not? Main memory, boot device and UART are configured before U-Boot,
> >>> no?
> >>
> >> It depends on what is running before U-Boot, so not necessarily.
> >>
> >> And speaking of boot device, consider the case where the system runs
> >> from eMMC and uses the HS200/HS400 modes, which need to switch bus mode
> >> using the pinmux driver.
> >>
> >> Is there a real-world use case where you would want to disable the
> >> pinmux driver ? And what is the benefit of that, except that it would
> >> cause all kinds of weird problems.
> > 
> > My H3ULCB-KF boots just fine [1] with CONFIG_PINCTRL_PFC=n, but I
> > personally don't have any use-case which I need to fulfill on a
> > Renesas reference design by disabling PFC.
> 
> And the eMMC and SDHI both work fine too in HS400/SDR104 modes ?
> They cannot, since you cannot switch the pinmux properties of the bus.
> What about the errors in the log below, they don't look quite fine.
> 
> > Rather, the motivation here is to ensure U-Boot builds fine with as
> > many randconfig results as possible, which is a standard practice in
> > Linux. I personally favor my solution, but I am also open minded if
> > the linker error is avoided by introducing a direct/reverse dependency
> > between PFC and another relevant R-Car3 Kconfig symbol.
> 
> I am fine with fixing randconfig build errors. My question here is
> whether it makes sense to allow U-Boot build without PFC support,
> since that would cause all kinds of problems. I am banking toward
> playing it safe and not allowing such an option at all. Thoughts ?

It looks like in Linux, PINCTRL is a fundamental feature selected
(i.e. *cannot* be disabled by users) by ARCH_RENESAS since v4.5 commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=26a7e06dfee9
("arm64: renesas: r8a7795: Add Renesas R8A7795 SoC support").

So, demanding a PFC-free U-Boot doesn't look reasonable to me.

Should PINCTRL be selected by CONFIG_RCAR_GEN3 as it is done in Linux?
One caveat is that PINCTRL currently depends on DM, so R-Car3 U-Boot
would become dependent on DM too, i.e. users won't have the option of
a legacy U-Boot anymore.

> > [1] U-Boot 2019.04-rc4-00100-g03ece61db8 (Apr 02 2019 - 17:23:57 +0200)
[..]

Best regards,
Eugeniu.