linux-kernel - Re: [PATCH] firmware: dmi: handle missing DMI data gracefully

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Date:   Tue, 17 Oct 2017 09:27:02 +0200
From:   Jean Delvare <jdelvare@...e.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] firmware: dmi: handle missing DMI data gracefully

Hi Ard,

On Thu, 12 Oct 2017 20:59:37 +0100, Ard Biesheuvel wrote:
> Currently, when booting a kernel with DMI support on a platform that has
> no DMI tables, the following output is emitted into the kernel log:
> 
>   [    0.128818] DMI not present or invalid.
>   ...
>   [    1.306659] dmi: Firmware registration failed.
>   ...
>   [    2.908681] dmi-sysfs: dmi entry is absent.
> 
> The first one is a pr_info(), but the subsequent ones are pr_err()s that
> complain about a condition that is not really an error to begin with.
> 
> So let's clean this up, and give up silently if dma_available is not set.

On the principle I agree, but you'll have to come up with an
implementation that links successfully:

ERROR: "dmi_available" [drivers/firmware/dmi-sysfs.ko] undefined!
scripts/Makefile.modpost:91: recipe for target '__modpost' failed
make[1]: *** [__modpost] Error 1
Makefile:1216: recipe for target 'modules' failed
make: *** [modules] Error 2

The reason is that dmi_available is not exported. The obvious solution
is to export it. Or maybe just turn the error message into a debug
message and assume the only reason it may reasonably happen is because
dmi isn't available in the first place. If dmi_kobj is missing for any
other reason then there's a much more important problem to solve anyway.

> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  drivers/firmware/dmi-sysfs.c | 3 +++
>  drivers/firmware/dmi_scan.c  | 6 ++----
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/firmware/dmi-sysfs.c b/drivers/firmware/dmi-sysfs.c
> index d5de6ee8466d..3a264cbbb5a6 100644
> --- a/drivers/firmware/dmi-sysfs.c
> +++ b/drivers/firmware/dmi-sysfs.c
> @@ -651,6 +651,9 @@ static int __init dmi_sysfs_init(void)
>  	int error;
>  	int val;
>  
> +	if (!dmi_available)
> +		return 0;
> +
>  	if (!dmi_kobj) {
>  		pr_err("dmi-sysfs: dmi entry is absent.\n");
>  		error = -ENODATA;
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index 783041964439..17a7425063c2 100644
> --- a/drivers/firmware/dmi_scan.c
> +++ b/drivers/firmware/dmi_scan.c
> @@ -715,10 +715,8 @@ static int __init dmi_init(void)
>  	u8 *dmi_table;
>  	int ret = -ENOMEM;
>  
> -	if (!dmi_available) {
> -		ret = -ENODATA;
> -		goto err;
> -	}
> +	if (!dmi_available)
> +		return 0;
>  
>  	/*
>  	 * Set up dmi directory at /sys/firmware/dmi. This entry should stay

-- 
Jean Delvare
SUSE L3 Support