[PATCH v3 1/3] Convert CONFIG_SYS_L2_PL310 to Kconfig

[Marek Vasut]

On 8/9/22 15:46, Tom Rini wrote:
> On Tue, Aug 09, 2022 at 01:32:24PM +0200, Pali Rohár wrote:
>> On Tuesday 09 August 2022 13:27:38 Marek Vasut wrote:
>>> On 8/9/22 13:21, Pali Rohár wrote:
>>>
>>> (reducing the CC list)
>>>
>>>> On Tuesday 09 August 2022 13:16:41 Marek Vasut wrote:
>>>>> On 8/9/22 12:58, Pali Rohár wrote:
>>>>>> On Tuesday 09 August 2022 12:07:00 Philip Oberfichtner wrote:
>>>>>>> This converts CONFIG_SYS_L2_PL310 to Kconfig.
>>>>>> ...
>>>>>>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>>>>>>> index 949ebb46ba..dde06bdd96 100644
>>>>>>> --- a/arch/arm/Kconfig
>>>>>>> +++ b/arch/arm/Kconfig
>>>>>>> @@ -488,6 +488,10 @@ config TPL_SYS_THUMB_BUILD
>>>>>>>     	   density. For ARM architectures that support Thumb2 this flag will
>>>>>>>     	   result in Thumb2 code generated by GCC.
>>>>>>> +config SYS_L2_PL310
>>>>>>> +	bool "ARM PL310 L2 cache controller"
> 
> This needs a depends on !SYS_L2CACHE_OFF.
> 
>>>>>>> +	help
>>>>>>> +	  Enable support for ARM PL310 L2 cache controller in U-Boot
>>>>>>>     config SYS_L2CACHE_OFF
>>>>>>>     	bool "L2cache off"
>>>>>>> diff --git a/arch/arm/mach-mvebu/include/mach/config.h b/arch/arm/mach-mvebu/include/mach/config.h
>>>>>>> index 4add0d9e10..0bba0a4cf9 100644
>>>>>>> --- a/arch/arm/mach-mvebu/include/mach/config.h
>>>>>>> +++ b/arch/arm/mach-mvebu/include/mach/config.h
>>>>>>> @@ -25,8 +25,6 @@
>>>>>>>     #define MV88F78X60 /* for the DDR training bin_hdr code */
>>>>>>>     #endif
>>>>>>> -#define CONFIG_SYS_L2_PL310
>>>>>>> -
>>>>>>>     #define MV_UART_CONSOLE_BASE		MVEBU_UART0_BASE
>>>>>>>     /* Needed for SPI NOR booting in SPL */
>>>>>>
>>>>>> This option is required for mvebu SoC and is not user (de)-selectable.
>>>>>> So please do not define it in each individual mvebu board. It would make
>>>>>> it harder to introduce a new mvebu board into U-Boot. Instead enable it
>>>>>> for mvebu SoCs like it was before this change. It can be done e.g. by
>>>>>> "select" Kconfig keyword in mvebu Kconfig file.
>>>>>
>>>>> Should it rather be 'default y if MVEBU' in that new PL310 Kconfig option ?
>>>>
>>>> No, because this is just default value of this option and still allows
>>>> end-user to de-select this option.
>>>>
>>>> "select" is IIRC the only way how to force Kconfig to always enable some
>>>> symbol without any option for end-user to disable it.
>>>>
>>>> At least I do not know a way how CONFIG_SYS_L2_PL310 symbol could decide
>>>> that it is required for CONFIG_MVEBU. Just symbol CONFIG_MVEBU can
>>>> decide that it requires CONFIG_SYS_L2_PL310 symbol (and not in opposite
>>>> direction).
>>>
>>> So why should the user be unable to deselect L2CC support on MVEBU ?
>>> I can very well disable L2CC support on MX6 and the platform works without
>>> it just fine. Maybe the MVEBU needs to be fixed to support the same instead
>>> ?
>>
>> Well, I'm not sure, currently it is non-deselectable option. Maybe it is
>> a bug... but at least change which is doing kconfig conversion should
>> not change behavior.
> 
> It's tricky to say when to "select" or just "default y if .." or "imply"
> a given option. It's not only a matter of "can you disable X and the
> system is functional" but "would you normally want to". There are
> certainly system bring-up cases and similar where you want to disable
> L2CC because you're tracking down something. But it's really a feature
> of the chip and expected to work and something we want enabled, and the
> scope of when it would be disabled is very very narrow. Looking back at
> the patch itself, the config.h files that enabled this are almost all a
> SoC-common file (ti_am335x_common.h should have been setting this I bet,
> something else for the TODO pile for me), so my thought is that it
> should be a select'd option, but if there's strong opinion that it's
> useful to make it easy to turn off when needed, imply'd instead by the
> various ARCH's in question instead.
> 
> That said, thinking about the missing dependency I listed above, that's
> how to disable L2 when needed, so perhaps select SYS_L2_PL310 if
> !SYS_L2CACHE_OFF under the various ARCH's is the right way.

Uh, I didn't realize we also had this SYS_L2CACHE_OFF .

In that case, the SYS_L2_PL310 selects the L2CC driver to be compiled in 
and that should likely be per-arch select indeed. And then 
SYS_L2CACHE_OFF should be 'default' or 'imply', so the user can 
configure it for the various hardware bring up cases ?

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