Re: [platforms: PATCH 1/7] Silicon/SynQuacer/PlatformDxe: Modify initialization of SdMmcOverride

[Marcin Wojtas <mw@semihalf.com>]

czw., 6 wrz 2018 o 16:31 Ard Biesheuvel <ard.biesheuvel@linaro.org> napisał(a):
>
> On 6 September 2018 at 16:26, Marcin Wojtas <mw@semihalf.com> wrote:
> > czw., 6 wrz 2018 o 16:04 Ard Biesheuvel <ard.biesheuvel@linaro.org> napisał(a):
> >>
> >> On 3 September 2018 at 06:53, Marcin Wojtas <mw@semihalf.com> wrote:
> >> > From: Tomasz Michalec <tm@semihalf.com>
> >> >
> >> > This patch changes way the EDKII_SD_MMC_OVERRIDE protocol
> >> > sturcture is allocated. Using AllocateZeroPool and then
> >> > seting callbacks in the structure allow driver to be immune to
> >> > adding new callbacks in SdMmcOveride protocol in future.
> >> >
> >>
> >> What is the point of this patch?
> >>
> >> Statically allocating the structure will zero initialize the members
> >> that are not initialized explicitly, but only the members that are
> >> known to exist at compile time.
> >>
> >
> > In such case this patch is really not needed.
> >
> >> I guess the idea of this patch is to work around the latter
> >> limitation, but unfortunately, using sizeof(EDKII_SD_MMC_OVERRIDE)
> >> puts you in the exact same situation.
> >
> > If the newly added callback are zero-initialized, the situation is
> > fine as they won't be executed.
> >
>
> Yes, but this patch does not change that situation at all.
>
> So please, explain which problem is fixed by this patch?

None, we only forgot, the static initializer will zero non-declared
fields by default.

>
> >>
> >> This is the reason I added the version field. New hooks should only be
> >> added after incrementing the version, and calling the new hooks should
> >> only occur if the runtime version of the protocol implementation is
> >> greater than or equal to the version where those hooks were first
> >> introduced.
> >>
> >
> > So even if the given SdMmcOverride protocol callback will be NULL for
> > Synquacer controller, is there still a risk that anything could be
> > broken without the version check?
> >
>
> Yes. In EDK2, you can combine binary drivers with drivers build from
> source. If a binary driver was built against an older version of the
> SdMmcOverride header, it may have non-NULL values in the locations of
> the new methods. This patch does not help against that scenario.

Indeed, this is why it will disappear from v2. So, when adding the new
callbacks, the version should be increased and checked in relevant
places of the main EDK2 driver, right?

Because a couple of the new callbacks are introduced, would it be ok,
to increment the version only once, i.e. v2 of the SdMmcOverride will
support 4 new routines?

Marcin