linux-kernel - Apparent Kconfig bug for Maxim 77650 driver

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Date:   Fri, 3 Jan 2020 00:36:42 -0500
From:   Paul Gazzillo <paul@...zz.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Lee Jones <lee.jones@...aro.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Apparent Kconfig bug for Maxim 77650 driver

It seems there is a Kconfig issue that causing a linking error for drivers/mfd/max77650.c.  It happens when CONFIG_MFD_MAX77650 is set (which controls drivers/mfd/max77650.c), but CONFIG_REGMAP_IRQ is not.  CONFIG_REMAP_IRQ controls drivers/base/regmap/regmap-irq.c, which has functions called by max77650.c.

In drivers/mfd/Kconfig, it looks like CONFIG_MFD_MAX77650 is meant to have "select CONFIG_REGMAP_IRQ" like several other configuration options from the same Kconfig file.

Steps to reproduce the bug for next-20191220 (also happens on other versions, e.g., v5.4.4):

  1. make allnoconfig  # using x86
  2. make menuconfig
    a. Enable device drivers->i2c support
    b. Enable device drivers->device tree and open firmware support
    c. Enable device drivers->multifunction devices->maxim MAX77650
  3. make  # should have a build error when linking vmlinux

This is the build error I get:

    ld: drivers/mfd/max77650.o: in function `max77650_i2c_probe':
    max77650.c:(.text+0xcb): undefined reference to `devm_regmap_add_irq_chip'
    ld: max77650.c:(.text+0xdb): undefined reference to `regmap_irq_get_domain'
    make: *** [Makefile:1079: vmlinux] Error 1

Is this a real bug or am I doing something wrong?

Best,
Paul