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 09:46:53 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Aisheng Dong <aisheng.dong@....com>
Cc:     Stephen Boyd <sboyd@...nel.org>, Abel Vesa <abel.vesa@....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" <allison@...utok.net>,
        "festevam@...il.com" <festevam@...il.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "info@...ux.net" <info@...ux.net>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "oleksandr.suvorov@...adex.com" <oleksandr.suvorov@...adex.com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "yuehaibing@...wei.com" <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 Wed, Jun 24, 2020 at 4:19 AM Aisheng Dong <aisheng.dong@....com> wrote:
> > 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.

The link error can be easily avoided by building all the clk support into
a single loadable module like below.

Hower this only works if all drivers that have a runtime dependency
on the clk driver support deferred probing or are built as loadable
modules as well and get loaded after the clk driver.

     Arnd

8<---
diff --git a/drivers/clk/imx/Makefile b/drivers/clk/imx/Makefile
index 928f874c73d2..638bc00f5731 100644
--- a/drivers/clk/imx/Makefile
+++ b/drivers/clk/imx/Makefile
@@ -1,6 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0

-obj-$(CONFIG_MXC_CLK) += \
+obj-$(CONFIG_MXC_CLK) := clk-imx.ko
+
+clk-imx-y += \
        clk.o \
        clk-busy.o \
        clk-composite-8m.o \
@@ -25,24 +27,24 @@ obj-$(CONFIG_MXC_CLK_SCU) += \
        clk-scu.o \
        clk-lpcg-scu.o

-obj-$(CONFIG_CLK_IMX8MM) += clk-imx8mm.o
-obj-$(CONFIG_CLK_IMX8MN) += clk-imx8mn.o
-obj-$(CONFIG_CLK_IMX8MP) += clk-imx8mp.o
-obj-$(CONFIG_CLK_IMX8MQ) += clk-imx8mq.o
-obj-$(CONFIG_CLK_IMX8QXP) += clk-imx8qxp.o clk-imx8qxp-lpcg.o
+clk-imx-$(CONFIG_CLK_IMX8MM) += clk-imx8mm.o
+clk-imx-$(CONFIG_CLK_IMX8MN) += clk-imx8mn.o
+clk-imx-$(CONFIG_CLK_IMX8MP) += clk-imx8mp.o
+clk-imx-$(CONFIG_CLK_IMX8MQ) += clk-imx8mq.o
+clk-imx-$(CONFIG_CLK_IMX8QXP) += clk-imx8qxp.o clk-imx8qxp-lpcg.o

-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-$(CONFIG_SOC_VF610)  += clk-vf610.o
+clk-imx-$(CONFIG_SOC_IMX1)   += clk-imx1.o
+clk-imx-$(CONFIG_SOC_IMX21)  += clk-imx21.o
+clk-imx-$(CONFIG_SOC_IMX25)  += clk-imx25.o
+clk-imx-$(CONFIG_SOC_IMX27)  += clk-imx27.o
+clk-imx-$(CONFIG_SOC_IMX31)  += clk-imx31.o
+clk-imx-$(CONFIG_SOC_IMX35)  += clk-imx35.o
+clk-imx-$(CONFIG_SOC_IMX5)   += clk-imx5.o
+clk-imx-$(CONFIG_SOC_IMX6Q)  += clk-imx6q.o
+clk-imx-$(CONFIG_SOC_IMX6SL) += clk-imx6sl.o
+clk-imx-$(CONFIG_SOC_IMX6SLL) += clk-imx6sll.o
+clk-imx-$(CONFIG_SOC_IMX6SX) += clk-imx6sx.o
+clk-imx-$(CONFIG_SOC_IMX6UL) += clk-imx6ul.o
+clk-imx-$(CONFIG_SOC_IMX7D)  += clk-imx7d.o
+clk-imx-$(CONFIG_SOC_IMX7ULP) += clk-imx7ulp.o
+clk-imx-$(CONFIG_SOC_VF610)  += clk-vf610.o