Red Hat Bugzilla – Bug 140558
nvram module does not support reading extra bank 128 bytes found in newer RTC implementations
Last modified: 2007-11-30 17:07:05 EST
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Description of problem:
Many of the newer (within the last few years) chipsets RTC's support
a second bank of 128 bytes of NVRAM. AMI BIOS presently uses some of
the registers in the second 128 bytes. Thus in order to back up the
NVRAM settings you need access to the second bank. Presently, this
is not supported in the nvram module. Someone backing up their NVRAM
settings using the current NVRAM module, may or may not, depending on
the chipset of their system get a good backup.
Chipsets that have this feature include the Intel E7521, E7500 and
Version-Release number of selected component (if applicable):
Steps to Reproduce:
On a machine using the E7521 chipset, and thus using the 6300ESB ICH
cat the contents of /dev/nvram to a file (after of course creating
the device and loading the module). Once having done look at the
size of the file. It should be 242 bytes (256 - 14 [i.e. both 128
byte banks, less the 14 bytes that comprise the RTC data region]), but
will be 114 bytes.
Actual Results: It only reads 114 bytes.
Expected Results: It should read 242 bytes.
I am attaching a patch that adds this functionality to the nvram
module, and the asm-i386/mc146818rtc.h header. It tries to detect
whether it a supporting ICH is being used, but that I think is the
weakest part of the patch.
Created attachment 107310 [details]
Adds support for extra 128 byte bank in RTC's NVRAM on some chipsets
Adds support in device to read extra 128 bytes on supporting devices.
Detection scheme I think is weak, would like any feed back that would make it
Just wondering if you have had a chance to look at this?
Where did you find out about the E7521, E7500, and E7501 chipset sizes? We are
using a E7505 based motherboard. Trying to decide if we should apply this patch
to our nvram module.
I read it in Intel's data sheets for the respective chipsets. I think they all
are all now available on Intel's web site (at the time the E7520 was not).
Basically, you lookup the info on the embedded RTC in the south bridge. I
suspect it is true of the E7505, but more experimenting on older mother boards
that happened to have the extended nvram area also. I suspect it does support
it, but know way of know short of adding the patch and giving a whirl or
reading the respective chipset's data sheet.
Closing out as wontfix in RHEL3, minimal interest, no upstream acceptance.
OK, its is a fact that many of the newer RTC's support 2 128 byte banks, yet
the nvram driver only shows the first bank, so you are saying there is no
interest in supporting what is pretty common hardware, or that my detection
algorithm was wrong (which I know to be the case)?
This patch, though needing improvement, helps in the area that linux is sorely
lacking, which is being able to configure linux BIOS's. Its only a step along
the way of course, as what is needed is mapps of different BIOS's nvram
utilization, but without being able to access the 2nd bank, your pretty much
Anyway, I can cary the patch along just fine, I just don't understand the lack
of upstream acceptance, nor the lack of interest. It would be nice if you
could enlighten me.