Re: [RFC PATCH v2 38/48] lib: Kconfig: add a config symbol for getting lmb memory map updates

[Tom Rini <trini@konsulko.com>]

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On Wed, Jul 24, 2024 at 09:40:35AM -0600, Simon Glass wrote:
> Hi Tom,
> 
> On Wed, 24 Jul 2024 at 08:52, Tom Rini <trini@konsulko.com> wrote:
> >
> > On Wed, Jul 24, 2024 at 08:37:14AM -0600, Simon Glass wrote:
> > > Hi Tom,
> > >
> > > On Tue, 23 Jul 2024 at 08:20, Tom Rini <trini@konsulko.com> wrote:
> > > >
> > > > On Tue, Jul 23, 2024 at 01:42:59PM +0100, Simon Glass wrote:
> > > > > Hi Sughosh,
> > > > >
> > > > > On Mon, 22 Jul 2024 at 13:59, Sughosh Ganu <sughosh.ganu@linaro.org> wrote:
> > > > > >
> > > > > > On Mon, 22 Jul 2024 at 18:00, Ilias Apalodimas
> > > > > > <ilias.apalodimas@linaro.org> wrote:
> > > > > > >
> > > > > > > On Fri, 5 Jul 2024 at 22:51, Tom Rini <trini@konsulko.com> wrote:
> > > > > > > >
> > > > > > > > On Thu, Jul 04, 2024 at 01:05:34PM +0530, Sughosh Ganu wrote:
> > > > > > > >
> > > > > > > > > Add a Kconfig symbol to enable getting updates on any memory map
> > > > > > > > > changes that might be done by the LMB module. This notification
> > > > > > > > > mechanism can then be used to have a synchronous view of allocated and
> > > > > > > > > free memory.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
> > > > > > > > > ---
> > > > > > > > > Changes since V1:
> > > > > > > > > * Change the description to highlight only LMB notifications.
> > > > > > > > > * Add a separate line for dependencies.
> > > > > > > > >
> > > > > > > > >  lib/Kconfig | 10 ++++++++++
> > > > > > > > >  1 file changed, 10 insertions(+)
> > > > > > > > >
> > > > > > > > > diff --git a/lib/Kconfig b/lib/Kconfig
> > > > > > > > > index 7eea517b3b..b422183a0f 100644
> > > > > > > > > --- a/lib/Kconfig
> > > > > > > > > +++ b/lib/Kconfig
> > > > > > > > > @@ -74,6 +74,16 @@ config HAVE_PRIVATE_LIBGCC
> > > > > > > > >  config LIB_UUID
> > > > > > > > >       bool
> > > > > > > > >
> > > > > > > > > +config MEM_MAP_UPDATE_NOTIFY
> > > > > > > > > +     bool "Get notified of any changes to the LMB memory map"
> > > > > > > > > +     depends on EVENT && LMB && EFI_LOADER
> > > > > > > > > +     default y
> > > > > > > > > +     help
> > > > > > > > > +       Enable this option to get notification on any changes to the
> > > > > > > > > +       memory that is allocated or freed by the LMB module. This will
> > > > > > > > > +       allow different modules that allocate memory or maintain a memory
> > > > > > > > > +       map to have a synchronous view of available and allocated memory.
> > > > > > > >
> > > > > > > > This needs to be select'd when it's going to be used, opting out of
> > > > > > > > making sure memory reservations are obeyed isn't a good idea.
> > > > > > >
> > > > > > > +1 which begs the question, do we need the config option at all ?
> > > > > >
> > > > > > The config symbol can be used for removing the code for platforms
> > > > > > which do not support EFI ?
> > > > >
> > > > > I am still of the so-far firm opinion that this can be done once,
> > > > > before booting, rather than maintaining two separate tables as we go.
> > > >
> > > > Did you see the part in the thread where he explained the multiple entry
> > > > points that would need to be kept in sync?
> > >
> > > Yes, but I'm not sure what they are, nor why a shared function cannot
> > > be called twice from two different places.
> >
> > Because we don't want to miss the third or fourth entry point down the
> > road. That's why going the other direction makes more sense I believe,
> > we won't have a future problem here because we designed with that in
> > mind.
> 
> You might be right, but I don't even know what we are referring to
> here...what are the two 'entry points'?

I would have to refer back to Sughosh's explanation to repeat it, sorry.

> My current belief is that we can set up the EFI memory table before
> booting, with a single pass through the table. Maintaining two
> independent tables as we go doesn't seem very useful. It is harder to
> test too.

You seem to be fixated on "booting" when at least part of the issue is
re-entering the EFI_LOADER. And since EFI_LOADER needs X/Y/Z as well, we
had much earlier rejected "make EFI_LOADER's memory model what
everything else uses".

-- 
Tom

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