[PATCH v3 1/3] Convert CONFIG_SYS_L2_PL310 to Kconfig

[Tom Rini]

On Tue, Aug 09, 2022 at 06:03:15PM +0200, Marek Vasut wrote:
> 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 .

Yeah, and it's also one of the odd "Enable this to turn oFF ..."
options, but I think in this case, that makes the most sense.  Note that
SYS_L2CACHE_OFF defaults to 'n' so do assume we have an L2 cache, and
also the option is ARM-specific.

> 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 ?

Yeah, I think we're in agreement here.

-- 
Tom
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 659 bytes
Desc: not available
URL: <https://lists.denx.de/pipermail/u-boot/attachments/20220809/cedc92cd/attachment.sig>