Re: Storing Non volatile variables on SD/NAND

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 18 September 2017 at 22:28, Udit Kumar <udit.kumar@nxp.com> wrote:
> Thanks Vladimir,
> With your design, you did delayed write to eMMC due to sharing with OS.  But it works for you:)
> Say if eMMC controllers offers you a status bit, if eMMC storage is being used for not. Then this
> could be possible to update at run time, both OS/UEFI needs to check and wait if controller is being used.

That is the problem right there. The nice thing about a firmware spec
is that you don't have to care about how it was implemented if you
adhere to the API rules. Imposing additional restrictions (such as
requiring the OS to be careful about not using the eMMC when it may be
in use by the firmware) defeats the purpose of using UEFI, since you
won't be able to use a generic OS anyway.


> For sure,  some synchronization issues need to be ironed out (or maybe I am just dreaming here).
>
> On part 2) where you forked VariableRuntime driver , could we think of updating VariableRuntime driver,
> to support non-XIP or memory mapped devices.
>

I think being able to support non-memorymapped FV volumes for the
variable store would be a big improvement. This does require changes
to both the FaultTolerantWrite drivers and the VariableRuntime
drivers, which both appear in PEI, DXE and SMM flavors, and require
thorough review due to the security impact bugs have in this layer, so
this is a rather large chunk of work to take on.