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

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Date:   Mon, 29 Jun 2020 15:04:40 +0800
From:   Dong Aisheng <dongas86@...il.com>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     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 Bergmann <arnd@...db.de>,
        Fabio Estevam <festevam@...il.com>,
        gregkh <gregkh@...uxfoundation.org>, info@...ux.net,
        Sascha Hauer <kernel@...gutronix.de>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Michael Turquette <mturquette@...libre.com>,
        oleksandr.suvorov@...adex.com,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Shawn Guo <shawnguo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, yuehaibing@...wei.com,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH V2 3/9] clk: imx: Support building SCU clock driver as module

On Thu, Jun 25, 2020 at 6:43 AM Stephen Boyd <sboyd@...nel.org> wrote:
>
> 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.

Yes, we can do that in clk/imx/Kconfig as follows theoretically.
config CLK_IMX6Q
        bool
        def_bool ARCH_MXC && ARM
        select MXC_CLK

But we have totally 15 platforms that need to change.
e.g.
drivers/clk/imx/Makefile
obj-$(CONFIG_SOC_IMX1)   += clk-imx1.o
obj-$(CONFIG_SOC_IMX21)  += clk-imx21.o
obj-$(CONFIG_SOC_IMX25)  += clk-imx25.o
obj-$(CONFIG_SOC_IMX27)  += clk-imx27.o
obj-$(CONFIG_SOC_IMX31)  += clk-imx31.o
obj-$(CONFIG_SOC_IMX35)  += clk-imx35.o
obj-$(CONFIG_SOC_IMX5)   += clk-imx5.o
obj-$(CONFIG_SOC_IMX6Q)  += clk-imx6q.o
obj-$(CONFIG_SOC_IMX6SL) += clk-imx6sl.o
obj-$(CONFIG_SOC_IMX6SLL) += clk-imx6sll.o
obj-$(CONFIG_SOC_IMX6SX) += clk-imx6sx.o
obj-$(CONFIG_SOC_IMX6UL) += clk-imx6ul.o
obj-$(CONFIG_SOC_IMX7D)  += clk-imx7d.o
obj-$(CONFIG_SOC_IMX7ULP) += clk-imx7ulp.o
obj-$(CONFIG_SOC_VF610)  += clk-vf610.o

Not sure if it's really worth to do that.
The easiest way to address this issue is just select it in
arch/arm/mach-imx/Kconfig,
then no need to change those 15 clock config options or just builtin
clk libraries.

Stephen,
which one do you prefer?

Regards
Aisheng