Re: [edk2-devel] [PATCH] Support skipping automatic BM enumeration

["Jeff Brasen" <jbrasen@nvidia.com>]

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Wouldn't having a variable that we create and delete on every boot put unnecessary stress on the SPI-NOR that the variable store lives on?
What about the alternative approach where we allow the platform code to modify the attributes of the auto created variable to disable it with hidden/!active but still match for detection purposes so that it doesn't delete and recreate the modified variable each boot? That way all the logic on what to disable can still be in the platform code and all the existing logic in the boot manager can stay basically the same?

What changes every boot that forces the variable to need to get modified?

I would assume the NOR driver is smart enough to not update a variable that is not changing.

The custom BDS could could only create the variable for this device if it does not exist.

[JB] The current flow with no changes in the boot manager would be as follows


  1.  Scan for instance of the boot option in the variables
  2.  It will not be found, so create a new boot option store it to a variable and update BootOrder
  3.  Platform code runs creates the options for the boot option it wants and writes those to variable store
  4.  Delete/disable the boot option in the variable store

When you reboot it won't find the variable so 1/2/4 will re-occur

The code that does this (1/2) is EfiBootManagerRefreshAllBootOption in BmBoot.c

If you modify the variable to disable it with hidden/not active it would delete that and create a new one as well as the code wouldn't recognize that is the same boot option.

If however we modify EfiBootManagerFindLoadOption to not compare the attributes (at least allow for differences in active and hidden) then the when it refreshes every thing it would see the match and not delete/create a new variable in the store and thus we wouldn't have changes every boot.


Thanks,

Andrew Fish

Thanks,

Jeff



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