linux-kernel - Re: [PATCH v3 1/3] misc/pvpanic: split-up generic and platform dependent code

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Date:   Fri, 12 Feb 2021 21:27:41 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Mihai Carabas <mihai.carabas@...cle.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Randy Dunlap <rdunlap@...radead.org>,
        Wang ShaoBo <bobo.shaobowang@...wei.com>
Subject: Re: [PATCH v3 1/3] misc/pvpanic: split-up generic and platform
 dependent code

On Fri, Feb 12, 2021 at 8:32 PM Mihai Carabas <mihai.carabas@...cle.com> wrote:
>
> Split-up generic and platform dependent code in order to be able to re-use
> generic event handling code in pvpanic PCI device driver in the next patches.
>
> The code from pvpanic.c was split in two new files:
> - pvpanic.c: generic code that handles pvpanic events
> - pvpanic-mmio.c: platform/bus dependent code
>
> Signed-off-by: Mihai Carabas <mihai.carabas@...cle.com>

> ---
>  drivers/misc/Kconfig                |   9 +--
>  drivers/misc/Makefile               |   2 +-
>  drivers/misc/pvpanic.c              | 111 ------------------------------------
>  drivers/misc/pvpanic/Kconfig        |  19 ++++++
>  drivers/misc/pvpanic/Makefile       |   8 +++
>  drivers/misc/pvpanic/pvpanic-mmio.c |  83 +++++++++++++++++++++++++++
>  drivers/misc/pvpanic/pvpanic.c      |  62 ++++++++++++++++++++
>  drivers/misc/pvpanic/pvpanic.h      |  17 ++++++


As mentioned, please use 'git format-patch -M' to make it easier to review

> +
> +config PVPANIC
> +       bool "pvpanic device support"
> +       help
> +         This option allows to select a specific pvpanic device driver.
> +         pvpanic is a paravirtualized device provided by QEMU; it lets
> +         a virtual machine (guest) communicate panic events to the host.
> +
> +config PVPANIC_MMIO
> +       tristate "pvpanic MMIO device support"
> +       depends on HAS_IOMEM && (ACPI || OF) && PVPANIC
> +       help
> +         This driver provides support for the MMIO pvpanic device.
...
> +#
> +obj-$(CONFIG_PVPANIC)          += pvpanic.o
> +obj-$(CONFIG_PVPANIC_MMIO)     += pvpanic-mmio.o

This solves the problem that Greg pointed out, but now the core pvpanic
driver is always built-in even when it is only used from loadable modules.

The easiest way to express what you actually want is with a Makefile
trick:

obj-$(CONFIG_PVPANIC)          += pvpanic.o pvpanic-pci.o
obj-$(CONFIG_PVPANIC_MMIO)     += pvpanic.o pvpanic-mmio.o

When you do this, pvpanic.o is built-in when at least one of its
users is built-in, and otherwise it a loadable module when there
is at least one user, but it will not be built twice or with the wrong
flags.

      Arnd