On 09/20/2017 12:39 PM, Ard Biesheuvel wrote:
On 20 September 2017 at 10:34, Udit Kumar <[email protected]> wrote:
When we want to have UEFI and OS accessing same media ,
Possibilities I see
1- Patch OS For status check of media (diversion from generic OS), Good case
will be modify low level driver.
But we may end up some surprises on synchronization.
2- no runtime service for OS . I guess this will not be possible
3- Way the Vladimir implemented for eMMC, This has risk of losing data in case
of AC power off.
4- update hardware with dual view (Ard suggestion)
5 - abstract direct block device access into a firmware service that
is exposed via a DXE_RUNTIME_DRIVER.
(along those lines)
6 - Build an emulated disk controller as well as NV region in el3 (or
el2) and export them to UEFI & the OS as real devices. Then trap/forward
requests to the actual storage device, which is "hidden". This AFAIK was
the basic idea behind the PS/2 emulation in x86/SMM. Again, probably not
a high performance option.
The UEFI spec allows you to expose entry points into a
DXE_RUNTIME_DRIVER module via a UEFI configuration table, and the OS
can use a driver that uses the abstracted device rather than the real
device. Performance is going to be terrible, probably, and lots of
things that are specific to SD/MMC will no longer work, but it is a
possibility nonetheless.
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