linux-kernel - RE: [PATCH] iwlwifi: work around reverse dependency on MEI

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Message-ID: <SA1PR11MB58258D60F7C1334471E2F434F26E9@SA1PR11MB5825.namprd11.prod.outlook.com>
Date:   Tue, 7 Dec 2021 13:19:10 +0000
From:   "Grumbach, Emmanuel" <emmanuel.grumbach@...el.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        "Coelho, Luciano" <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>
CC:     Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Beker, Ayala" <ayala.beker@...el.com>,
        "Korenblit, Miriam Rachel" <miriam.rachel.korenblit@...el.com>,
        "Berg, Johannes" <johannes.berg@...el.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] iwlwifi: work around reverse dependency on MEI

Hi Arend,

> Subject: [PATCH] iwlwifi: work around reverse dependency on MEI
> 
> From: Arnd Bergmann <arnd@...db.de>
> 
> If the iwlmei code is a loadable module, the main iwlwifi driver cannot be
> built-in:
> 
> x86_64-linux-ld: drivers/net/wireless/intel/iwlwifi/pcie/trans.o: in function
> `iwl_pcie_prepare_card_hw':
> trans.c:(.text+0x4158): undefined reference to `iwl_mei_is_connected'
> 
> Unfortunately, Kconfig enforces the opposite, forcing the MEI driver to not
> be built-in if iwlwifi is a module.
> 
> There is no easy way to express the correct dependency in Kconfig, this is the
> best workaround I could come up with, turning CONFIG_IWLMEI into a 'bool'
> symbol, and spelling out the exact conditions under which it may be enabled,
> and then using Makefile logic to ensure it is built-in when iwlwifi is.
> 
> A better option would be change iwl_mei_is_connected() so it could be
> called from iwlwifi regardless of whether the mei driver is reachable, but that
> requires a larger rework in the driver.

I can try to do that but I don't really see how..
I can't really make a function that would behave differently based on whether the symbol is available or not.

> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/net/wireless/intel/iwlwifi/Kconfig      | 6 +++---
>  drivers/net/wireless/intel/iwlwifi/Makefile     | 3 +--
>  drivers/net/wireless/intel/iwlwifi/mei/Makefile | 4 +++-
>  3 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/Kconfig
> b/drivers/net/wireless/intel/iwlwifi/Kconfig
> index cf1125d84929..474afc6f82a8 100644
> --- a/drivers/net/wireless/intel/iwlwifi/Kconfig
> +++ b/drivers/net/wireless/intel/iwlwifi/Kconfig
> @@ -93,10 +93,10 @@ config IWLWIFI_BCAST_FILTERING
>  	  expect incoming broadcasts for their normal operations.
> 
>  config IWLMEI
> -	tristate "Intel Management Engine communication over WLAN"
> -	depends on INTEL_MEI
> +	bool "Intel Management Engine communication over WLAN"
> +	depends on INTEL_MEI=y || INTEL_MEI=IWLMVM
> +	depends on IWLMVM=y || IWLWIFI=m
>  	depends on PM
> -	depends on IWLMVM
>  	help
>  	  Enables the iwlmei kernel module.

Johannes suggested to make IWLMVM depend on IWLMEI || !IWLMEI
That worked as well, I just had issues with this in our internal backport based tree.
I need to spend a bit more time on this, but I admit my total ignorance in Kconfig's dialect.


> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/Makefile
> b/drivers/net/wireless/intel/iwlwifi/Makefile
> index 75a703eb1bdf..c117e105fe5c 100644
> --- a/drivers/net/wireless/intel/iwlwifi/Makefile
> +++ b/drivers/net/wireless/intel/iwlwifi/Makefile
> @@ -29,7 +29,6 @@ iwlwifi-$(CONFIG_IWLWIFI_DEVICE_TRACING) += iwl-
> devtrace.o  ccflags-y += -I$(src)
> 
>  obj-$(CONFIG_IWLDVM)	+= dvm/
> -obj-$(CONFIG_IWLMVM)	+= mvm/
> -obj-$(CONFIG_IWLMEI)	+= mei/
> +obj-$(CONFIG_IWLMVM)	+= mvm/ mei/
> 
>  CFLAGS_iwl-devtrace.o := -I$(src)
> diff --git a/drivers/net/wireless/intel/iwlwifi/mei/Makefile
> b/drivers/net/wireless/intel/iwlwifi/mei/Makefile
> index 8e3ef0347db7..98b561c3820f 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mei/Makefile
> +++ b/drivers/net/wireless/intel/iwlwifi/mei/Makefile
> @@ -1,5 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> -obj-$(CONFIG_IWLMEI)	+= iwlmei.o
> +ifdef CONFIG_IWLMEI
> +obj-$(CONFIG_IWLWIFI)	+= iwlmei.o
> +endif
>  iwlmei-y += main.o
>  iwlmei-y += net.o
>  iwlmei-$(CONFIG_IWLWIFI_DEVICE_TRACING) += trace.o
> --
> 2.29.2