Re: [edk2-devel] [PATCH edk2-platforms 1/4] Ext4Pkg: Use depex for unicode collation protocols

["Ard Biesheuvel" <ardb@kernel.org>]

On Fri, 17 Feb 2023 at 18:31, Pedro Falcato <pedro.falcato@gmail.com> wrote:
>
> On Fri, Feb 17, 2023 at 3:38 PM Marvin Häuser <mhaeuser@posteo.de> wrote:
> >
> >
> > > On 17. Feb 2023, at 16:17, Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > So the FAT driver will happily load, but then fail in an obscure
> > > manner when being started on a controller handle, in a way that is
> > > indistinguishable (afict) from a partition that has not FAT file
> > > system in the first place.
> > >
> > > So it doesn't look fine to me at all, tbh. If the collation protocols
> > > are required, we should check for them in supported(), and make a lot
> > > of noise in a DEBUG build if the failure condition is an unexpected
> > > one, i.e., some additional protocol we dependent on (even though we
> > > pretend to be a UEFI driver)  does not exist.
>
> Hi Ard, Marvin,
>
> First of all, thank you for raising this issue and sending a patch. I
> had been quietly following the thread while trying to get my ideas
> straight.
>
> >
> > Right, I meant the approach to rely on the UEFI Driver Binding handling to defer locating UC, not the exact implementation. Sounds good.
> >
> > @Pedro What do you think?
> >
>
> I think deferring the Unicode collation init to Start()/Supported() is
> a good idea. I believe there's good value in keeping Ext4Dxe a
> UEFI_DRIVER.
> I was trying to come up with reasons why this would not work (in a
> general UEFI-spec sense, not only in Tiano, but for instance if you
> would ever want to plug this into i.e u-boot's EFI implementation).
> As far as I can tell, there doesn't seem to be any? At least from a PI
> PoV things should only get Start()'d in BDS right? And since other
> PI-unaware implementations don't know what DXE or DXE_DRIVERs are,
> it's not like that would fix those use cases.
>

Indeed. I suspect this was moved into Start() rather than Supported()
because the latter is called much more often by the driver model
logic. However, given that we populate a global variable with a
protocol pointer, we can simply skip this logic once we have managed
to set it once.