linux-kernel - Re: [PATCH v9 5/8] x86/boot: Add get_acpi_rsdp() to parse RSDP in cmdlien from kexec

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Date:   Mon, 22 Oct 2018 15:30:51 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Baoquan He <bhe@...hat.com>
CC:     <dyoung@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "msys.mizuma@...il.com" <msys.mizuma@...il.com>,
        "Indoh, Takao" <indou.takao@...itsu.com>,
        "Cao, Jin" <caoj.fnst@...fujitsu.com>
Subject: Re: [PATCH v9 5/8] x86/boot: Add get_acpi_rsdp() to parse RSDP in
 cmdlien from kexec

On Mon, Oct 22, 2018 at 02:06:13PM +0800, Baoquan He wrote:
>On 10/22/18 at 05:30am, Fan, Chao wrote:
>> >> +static void get_acpi_rsdp(acpi_physical_address *rsdp_addr)
>> >> +{
>> >> +#ifdef CONFIG_KEXEC
>> >> +	unsigned long long res;
>> >> +	int len = 0;
>> >> +	char *val;
>> >> +
>> >> +	val = malloc(20);
>> >
>> >Why is the length 20? Defined a macro?
>> >
>> 
>> Not a calculation, if it's enough to store the address, that will be OK.
>
>Sorry, I didn't catch. It's 16 in setup_acpi_rsdp() of
>drivers/acpi/osl.c . What does 'that' mean?

The second parameter of kstrtoull(), the 16 you mentioned means
hexadecimal, not the length.
I checked my host and guest, the value are ACPI20=0xbfbfa014, ACPI20=0xdb807000.
The length of memory is 8. Well the max memory address is 16, add
"0x" and '\0' is 19. So I set it as 20.
I am not sure whether 8 is enough for the address, if OK, 11 will
be enough, or 19 is OK.
If my understanding is wrong, please tell me.

Thanks,
Chao Fan

>
>Wondering why not making it 200, it's also enough to store the address.
>
>