linux-kernel - Re: [PATCH] r8169: fix building with CONFIG_LEDS

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Message-Id: <b310230b-f20b-489a-97ed-908df193a942@app.fastmail.com>
Date: Wed, 03 Jan 2024 13:45:40 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Heiner Kallweit" <hkallweit1@...il.com>,
 "Arnd Bergmann" <arnd@...nel.org>, "David S . Miller" <davem@...emloft.net>,
 "Eric Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>,
 "Paolo Abeni" <pabeni@...hat.com>
Cc: Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org,
 "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
 "Lee Jones" <lee@...nel.org>
Subject: Re: [PATCH] r8169: fix building with CONFIG_LEDS_CLASS=m

On Wed, Jan 3, 2024, at 12:33, Heiner Kallweit wrote:
> On 03.01.2024 11:26, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>> 
>> When r8169 is built-in but the LED support is a loadable module, the
>> new code to drive the LED now causes a link failure:
>> 
>> ld: drivers/net/ethernet/realtek/r8169_leds.o: in function `rtl8168_init_leds':
>> r8169_leds.c:(.text+0x36c): undefined reference to `devm_led_classdev_register_ext'
>> 
>> Add a Kconfig dependency to prevent the broken configuration but still
>> allow having the network code built-in as long as CONFIG_LEDS_TRIGGER_NETDEV
>> is disabled, regardless of CONFIG_LEDS_CLASS.
>> 
> The proposed change is more of a workaround IMO. A proper fix (in LED 
> subsystem)
> has been submitted, but it's not reviewed/applied yet. And I don't 
> think building
> r8169 should depend on support for an optional feature.
> This fix would also allow to remove Kconfig dependencies similar to the 
> one
> proposed here from other drivers. Link to submitted fix:
>
> https://lore.kernel.org/linux-leds/0f6f432b-c650-4bb8-a1b5-fe3372804d52@gmail.com/T/#u

I think that is a much worse workaround, as this just leads to
a feature silently not working even when it is enabled (as loadable
module), and hiding other dependency problems where drivers
actually require the LED support to do something useful.

IS_REACHABLE() is pretty much always a bad idea because of this.

If you want the LED support in r8169_leds to be optional, I would
suggest adding a separate Kconfig symbol for that, either user
visible or hidden, and have the correct Kconfig dependencies
for the new symbol, something like the change below (untested).

     Arnd

8<---
diff --git a/drivers/net/ethernet/realtek/Kconfig b/drivers/net/ethernet/realtek/Kconfig
index fd3f18b328de..b54aae30b3c1 100644
--- a/drivers/net/ethernet/realtek/Kconfig
+++ b/drivers/net/ethernet/realtek/Kconfig
@@ -114,4 +114,9 @@ config R8169
          To compile this driver as a module, choose M here: the module
          will be called r8169.  This is recommended.
 
+config R8169_LEDS
+       def_bool y
+       depends on LEDS_TRIGGER_NETDEV && R8169
+       depends on !(R8169=y && LEDS_CLASS=m)
+
 endif # NET_VENDOR_REALTEK
diff --git a/drivers/net/ethernet/realtek/Makefile b/drivers/net/ethernet/realtek/Makefile
index adff9ebfbf2c..635491d8826e 100644
--- a/drivers/net/ethernet/realtek/Makefile
+++ b/drivers/net/ethernet/realtek/Makefile
@@ -6,8 +6,6 @@
 obj-$(CONFIG_8139CP) += 8139cp.o
 obj-$(CONFIG_8139TOO) += 8139too.o
 obj-$(CONFIG_ATP) += atp.o
-r8169-objs += r8169_main.o r8169_firmware.o r8169_phy_config.o
-ifdef CONFIG_LEDS_TRIGGER_NETDEV
-r8169-objs += r8169_leds.o
-endif
+r8169-y += r8169_main.o r8169_firmware.o r8169_phy_config.o
+r8169-$(CONFIG_R8169_LEDS) += r8169_leds.o
 obj-$(CONFIG_R8169) += r8169.o
diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
index 05ba5f743af2..f3321299b2fa 100644
--- a/drivers/net/ethernet/realtek/r8169_main.c
+++ b/drivers/net/ethernet/realtek/r8169_main.c
@@ -5356,11 +5356,10 @@ static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
        if (rc)
                return rc;
 
-#if IS_REACHABLE(CONFIG_LEDS_CLASS) && IS_ENABLED(CONFIG_LEDS_TRIGGER_NETDEV)
-       if (tp->mac_version > RTL_GIGA_MAC_VER_06 &&
+       if (IS_ENABLED(CONFIG_R8169_LEDS) &&
+           tp->mac_version > RTL_GIGA_MAC_VER_06 &&
            tp->mac_version < RTL_GIGA_MAC_VER_61)
                rtl8168_init_leds(dev);
-#endif
 
        netdev_info(dev, "%s, %pM, XID %03x, IRQ %d\n",
                    rtl_chip_infos[chipset].name, dev->dev_addr, xid, tp->irq);