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dmi_scan: add comments on dmi_present() and the loop in dmi_scan_machine()

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My previous refactoring in commit 79bae42d51 ("dmi_scan: refactor
dmi_scan_machine(), {smbios,dmi}_present()") resulted in slightly tricky
code (though I think it's more elegant).  Explain what it's doing.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ben Hutchings 2013-07-31 13:53:30 -07:00 committed by Linus Torvalds
parent 62c610460d
commit d39de28c95
1 changed files with 14 additions and 0 deletions
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14
drivers/firmware/dmi_scan.c
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@ -419,6 +419,13 @@ static void __init dmi_format_ids(char *buf, size_t len)
dmi_get_system_info(DMI_BIOS_DATE));
}
/*
* Check for DMI/SMBIOS headers in the system firmware image. Any
* SMBIOS header must start 16 bytes before the DMI header, so take a
* 32 byte buffer and check for DMI at offset 16 and SMBIOS at offset
* 0. If the DMI header is present, set dmi_ver accordingly (SMBIOS
* takes precedence) and return 0. Otherwise return 1.
*/
static int __init dmi_present(const u8 *buf)
{
int smbios_ver;
@ -506,6 +513,13 @@ void __init dmi_scan_machine(void)
if (p == NULL)
goto error;
/*
* Iterate over all possible DMI header addresses q.
* Maintain the 32 bytes around q in buf. On the
* first iteration, substitute zero for the
* out-of-range bytes so there is no chance of falsely
* detecting an SMBIOS header.
*/
memset(buf, 0, 16);
for (q = p; q < p + 0x10000; q += 16) {
memcpy_fromio(buf + 16, q, 16);