linux-kernel - Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry

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Date:   Thu, 15 Dec 2016 12:28:56 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Eric Biederman <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        kexec@...ts.infradead.org
Subject: Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry_point to
 kexec'ed kernel

Hi Andy,

On Fri,  2 Dec 2016 21:54:16 +0200, Andy Shevchenko wrote:
> Until now kexec'ed kernel has no clue where to look for DMI entry point.
> 
> Pass it via kernel command line parameter in the same way as it's done for ACPI
> RSDP.

I am no kexec expert but this confuses me. Shouldn't the second kernel
have access to the EFI systab as the first kernel does? It includes
many more pointers than just ACPI and DMI tables, and it would seem
inconvenient to have to pass all these addresses individually
explicitly.

Adding Eric to Cc for his opinion.

> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  5 +++++
>  drivers/firmware/dmi_scan.c                     | 14 ++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index be2d6d0..94f219f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -843,6 +843,11 @@
>  			The filter can be disabled or changed to another
>  			driver later using sysfs.
>  
> +	dmi_entry_point=	[DMI,EFI,KEXEC]
> +			Pass the DMI entry point to the kernel, mostly used
> +			on machines running EFI runtime service to boot the
> +			second kernel for kdump.
> +
>  	drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
>  			Broken monitors, graphic adapters, KVMs and EDIDless
>  			panels may send no or incorrect EDID data sets.
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index b88def6..215843f 100644
> --- a/drivers/firmware/dmi_scan.c
> +++ b/drivers/firmware/dmi_scan.c
> @@ -595,8 +595,22 @@ static int __init dmi_smbios3_present(const u8 *buf)
>  	return 1;
>  }
>  
> +#ifdef CONFIG_KEXEC
> +static unsigned long dmi_entry_point;
> +static int __init setup_dmi_entry_point(char *arg)
> +{
> +	return kstrtoul(arg, 16, &dmi_entry_point);
> +}
> +early_param("dmi_entry_point", setup_dmi_entry_point);
> +#endif
> +
>  static resource_size_t __init dmi_get_entry_point(void)
>  {
> +#ifdef CONFIG_KEXEC
> +	if (dmi_entry_point)
> +		return dmi_entry_point;
> +#endif
> +
>  	if (efi_enabled(EFI_CONFIG_TABLES)) {
>  		/*
>  		 * According to the DMTF SMBIOS reference spec v3.0.0, it is


-- 
Jean Delvare
SUSE L3 Support