From: Ed Tanous <edtanous@google.com>
To: Patrick Williams <patrick@stwcx.xyz>
Cc: openbmc@lists.ozlabs.org, Benjamin Fair <benjaminfair@google.com>,
Michael Shen <gpgpgp@google.com>
Subject: Re: Propose a new application for reading DIMM SPD directly
Date: Wed, 9 Feb 2022 14:45:09 -0800 [thread overview]
Message-ID: <CAH2-KxA6MhNXUs+KXAjHTcJe1gWyGwfL+OUQBuCfQnPMSX7GZQ@mail.gmail.com> (raw)
In-Reply-To: <YgQuzD9AkrqstygH@heinlein>
On Wed, Feb 9, 2022 at 1:14 PM Patrick Williams <patrick@stwcx.xyz> wrote:
>
> On Wed, Feb 09, 2022 at 12:20:00PM -0800, Ed Tanous wrote:
> > On Wed, Feb 9, 2022 at 11:56 AM Patrick Williams <patrick@stwcx.xyz> wrote:
> > > On Tue, Feb 08, 2022 at 04:23:12PM +0800, Michael Shen wrote:
> > > > On Tue, Feb 8, 2022 at 3:11 PM Patrick Williams <patrick@stwcx.xyz> wrote:
> > > > > On Tue, Feb 08, 2022 at 01:10:37PM +0800, Michael Shen wrote:
>
> > > > BIOS owns the MUX select pin and it can decide who owns the SPD(I2C/I3C) bus.
> > > > From my understanding, BIOS only needs to read SPD during the POST stage.
> > > > For the rest of time, BIOS will hand over the SPD bus to BMC.
> > >
> > > That seems like it might work. You'll have to deal with the time when the BIOS
> > > has the mux in the BMC code somehow. Ideally I'd ask for the mux select to also
> > > be fed to the BMC as an input GPIO so that you can differentiate between "we
> > > don't own the mux" and "all the devices are NAKing us".
> >
> > This seems like a nitty gritty design detail that's best handled in
> > code when we review it. I think the important bit here is that there
> > are paths where this could work without a significant design issue.
>
> Just one subtlety. I wouldn't expect this, necessarily, to be in _our_ design
> and/or code, except that we'd want to document the GPIO line like we do all
> others. I was trying to hint that "if I were involved in this hardware design,
> I'd ask for...". If you leave it out, I'm sure it'll work _most_ of the time
> just fine and it'll be your problem to debug it when it doesn't.
Understood.
>
> --
> Patrick Williams
next prev parent reply other threads:[~2022-02-09 22:46 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-08 5:10 Propose a new application for reading DIMM SPD directly Michael Shen
2022-02-08 7:11 ` Patrick Williams
2022-02-08 8:23 ` Michael Shen
2022-02-09 19:56 ` Patrick Williams
2022-02-09 20:20 ` Ed Tanous
2022-02-09 21:14 ` Patrick Williams
2022-02-09 22:45 ` Ed Tanous [this message]
2022-02-11 0:40 ` Michael Shen
2022-02-11 21:21 ` Zbigniew, Lukwinski
2022-02-14 22:17 ` Benjamin Fair
2022-02-15 1:50 ` Michael Shen
2022-02-15 20:39 ` Zbigniew, Lukwinski
2022-02-17 3:59 ` Michael Shen
2022-02-21 12:07 ` Zbigniew, Lukwinski
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