[PATCH] ARM64: Kconfig: Fix the missing hi655x common clk

On Mon, Jun 12, 2017 at 11:38 AM, Daniel Lezcano
[off-list ref] wrote:

On Fri, Jun 09, 2017 at 10:48:13PM +0200, Arnd Bergmann wrote:

quoted

On Fri, Jun 9, 2017 at 10:15 PM, John Stultz [off-list ref] wrote:

quoted

On Fri, Jun 9, 2017 at 1:06 PM, Arnd Bergmann [off-list ref] wrote:

quoted

On Fri, Jun 9, 2017 at 5:46 PM, Daniel Lezcano
[off-list ref] wrote:

Yes, but I'm not sure this is the right patch either. We tend to not
use 'select' for user-visible drivers, and most hisilicon platforms
won't need this driver.

I think it would be more consistent to add this to the defconfig
and regard it as a user error when the driver is disabled on a
machine that needs it.

Maybe the select is not exactly in the right place, but I don't really
feel like a pmic on an SoC is a "user-visible driver". I deal with the
board often and when the new dependency was made on the clk, I would
have never have found it on my own w/o Ulf and Daniel pointing out
what I needed to enable.

What I meant is that the Kconfig option is user-visible. On a very high
level, this is a result of arch/arm64/Kconfig.platforms listing only
very broad categories of SoCs, in many cases only the manufacturers
of very different chip families, which then control the visibility of the
individual Kconfig items for things like pinctrl or clk.

I now see that MFD_HI655X_PMIC is the top-level driver that you
have to select before enabling COMMON_CLK_HI655X, so the
patch is actually broken unless it actually selects both.

How about simply adding a 'default MFD_HI655X_PMIC' to
COMMON_CLK_HI655X to enable it unless it is explicitly
turned off?

Actually, I share John's opinion.

Ideally when we choose a platform, all the relevants devices configuration
options should be selected automatically from a single topmost node of a tree
(platform selection) to all the nodes corresponding to the devices, leaving the
user to select one simple option without knowledge of the SoC hardware
internals.

If the user is expert in the platform and knows exactly what he does, then he
can select an _EXPERT_ like option and be able to disable some drivers.

It is how I tend to write the Kconfig options, so the 'default MFD_HI655X_PMIC'
is confusing for me. Wouldn't make sense to select COMMON_CLK_HI655X when
MFD_HI655X_PMIC is enabled?

I don't think it's that easy. When you do that, MFD_HI655X_PMIC gains
a dependency on COMMON_CLK and will again cause a warning on
machines that disable that during compile testing.

Using 'select' for user-selectable options generally leads to problems,
and you are better off avoiding it. If you want to make the symbol impossible
to turn off for non-EXPERT configurations, you can write it like

config COMMON_CLK_HI655X
        tristate "Clock driver for Hi655x" if EXPERT
        depends on (MFD_HI655X_PMIC || COMPILE_TEST)
        depends on REGMAP
        default MFD_HI655X_PMIC

That way the option is completely hidden for non-EXPERT,
but still has the right default otherwise, and the dependencies
are tracked right for compile-testing.

     Arnd