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

[Dirk Behme]

On 03.04.2019 14:11, Marek Vasut wrote:
> On 4/2/19 7:02 PM, Eugeniu Rosca wrote:
>> 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.
> 
> That's sensible.
> 
>> 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.
> 
> Non-DM operation is not supported anyway, the direction is toward DM/DT
> support. Ultimately, it should be possible to have a single U-Boot
> binary and just exchange the DT to support different boards.
> 
> My concern is with the size of the PFC tables, they are massive, sparse
> and keep growing, but that's a different topic.
> 
> That said, what about making the GPIO driver depend on PFC driver and
> then have Gen3 select PFC by default in Kconfig ?


Of course, you can add such a dependency in Kconfig. But that's not the 
question here and won't fix the issue:

It won't fix the issue that we have code encapsulated with a CONFIG_* 
option and a caller which is not encapsulated with this.

To fix this with your proposal, you need to merge CONFIG_PINCTRL_PFC and 
CONFIG_RCAR_GPIO to *one* CONFIG_RCAR_PINCTRL_PFC_GPIO (or whatever) to 
ensure that both, the function definition *and* the caller are 
encapsulated by the *same* CONFIG switch. But this sounds somehow quite 
strange to me ...

Best regards

Dirk