linux-kernel - RE: [PATCH V2 3/9] clk: imx: Support building SCU clock driver as module

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Date:   Wed, 24 Jun 2020 15:43:00 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Abel Vesa <abel.vesa@....com>, Aisheng Dong <aisheng.dong@....com>,
        Andy Duan <fugang.duan@....com>,
        Anson Huang <anson.huang@....com>,
        Daniel Baluta <daniel.baluta@....com>,
        Leonard Crestez <leonard.crestez@....com>,
        Peng Fan <peng.fan@....com>,
        Stefan Agner <stefan.agner@...adex.com>, allison@...utok.net,
        arnd@...db.de, festevam@...il.com, gregkh@...uxfoundation.org,
        info@...ux.net, kernel@...gutronix.de,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        mturquette@...libre.com, oleksandr.suvorov@...adex.com,
        s.hauer@...gutronix.de, sfr@...b.auug.org.au, shawnguo@...nel.org,
        tglx@...utronix.de, yuehaibing@...wei.com
Cc:     dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V2 3/9] clk: imx: Support building SCU clock driver as module

Quoting Aisheng Dong (2020-06-23 19:59:09)
> > > > > -       bool
> > > > > -       def_bool ARCH_MXC
> > > > > +       tristate "IMX clock"
> > > > > +       depends on ARCH_MXC
> > > > >
> > > > > But user can still set MXC_CLK to be m, either via make menuconfig
> > > > > or
> > > > defconfig.
> > > >
> > > > Isn't that what we want?
> > >
> > > No, if user set MXC_CLK to m, the build will break for i.MX6&7.
> > >
> > > > Why does ARCH_MXC being enabled mandate that it is builtin? Is some
> > > > architecture level code calling into the clk driver?
> > >
> > >
> > > It's mainly because there's no Kconfig options for i.MX6 &7 clock drivers.
> > > It just reuses ARCH config CONFIG_SOC_XXX which can only be y.
> > > e.g.
> > > obj-$(CONFIG_SOC_IMX6Q)  += clk-imx6q.o
> > > obj-$(CONFIG_SOC_IMX6SL) += clk-imx6sl.o
> > > obj-$(CONFIG_SOC_IMX7ULP) += clk-imx7ulp.o
> > > obj-$(CONFIG_SOC_VF610)  += clk-vf610.o ..
> > >
> > > If setting MXC_CLK to m, the platform clock drivers will fail to build
> > > due to miss to find symbols defined in the common clock library by
> > > CONFIG_MXC_CLK.
> > > So we have to avoid users to be able to config MXC_CLK to m for i.MX6&7.
> > > Only depends on ARCH_MXC mean user still can set it to m.
> > 
> > I think for i.MX6/7, although MXC_CLK is tristate, but it is selected by
> > ARCH_MXC which is always "y", so MXC_CLK can ONLY be "y" even it is explicitly
> > set to "m" in imx_v6_v7_defconfig file. So that means MXC_CLK can ONLY
> > support built-in for i.MX6/7 SoCs, and that is what we want?
> > 
> 
> Yes, I'm trying to explain to Stephen why we have to select MXC_CLK in ARCH_MXC
> And what issues we will met if not select it.
> 

Why aren't there options to enable clk-imx6q and clk-imx6sl in the
clk/imx/Kconfig file? Those can be bool or tristate depending on if the
SoC drivers use CLK_OF_DECLARE or not and depend on the mxc-clk library
and SoC config we have in the makefile today.