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Tue, 8 Feb 2022 02:11:30 -0500 (EST) Date: Tue, 8 Feb 2022 01:11:29 -0600 From: Patrick Williams To: Michael Shen Subject: Re: Propose a new application for reading DIMM SPD directly Message-ID: References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="8WI4CJN/1CmqA8yt" Content-Disposition: inline In-Reply-To: X-BeenThere: openbmc@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development list for OpenBMC List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: openbmc@lists.ozlabs.org Errors-To: openbmc-bounces+openbmc=archiver.kernel.org@lists.ozlabs.org Sender: "openbmc" --8WI4CJN/1CmqA8yt Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Feb 08, 2022 at 01:10:37PM +0800, Michael Shen wrote: > Hi Openbmc, >=20 > We would like to propose an application that directly reads the DIMM > SPD over HW interface(mostly I2C/I3C). Who is "we"? > If I understand correctly, the main method for obtaining the SPD > information in openbmc is from SMBIOS which is prepared by BIOS. And > We are exploring another way that excludes the involvement of BIOS. Unless you're proposing that the BIOS itself comes to the BMC to get the SPD data, I'm somewhat surprised you could come up with a hardware design to ma= ke this work. Due to the number of DIMM channels and the limited number of CS= pins on JEDEC DIMMs, you're going to have muxes on the bus somewhere. Mixing mu= xes and multi-master access is pretty problematic. Either the BIOS and BMC are fighting over the mux, which is going to mess with the mux driver's view of= the world, or you've got one mux for each in which case you're switching masters onto a bus, which violates a few i2c design rules. > The architecture of this application will be similar to the > openbmc/smbios-mdr (the dimm part). The main difference will be the > data source (changed from SMBIOS to SPD). >=20 > Currently the code is still being implemented, and we plan to support > DDR5 SPD first, then expand to other DDR generation(if needed). Hopefully you're leveraging the existing kernel drivers for reading SPD EEP= ROMs. This creates you a sysfs file containing the whole of the EEPROM content. = You'd just need to write a parser for JEDEC SPD format data. You should take a look at what is already existing in fru-device (part of entity-manager repository). This is already doing this for IPMI-format EEP= ROM data. We should be able to replicate/enhance this code, in the same reposi= tory, to handle SPD format. > If this proposal looks good to you, please help to create a repo for > this application. >=20 > Best, > Michael --=20 Patrick Williams --8WI4CJN/1CmqA8yt Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEBGD9ii4LE9cNbqJBqwNHzC0AwRkFAmICF58ACgkQqwNHzC0A wRnggA//RmYGsgoN1vzpyYc3+us5cMFFErgvZS1Iv9Z6zO52TbBrbK2B23gnYCZN Ly592Pm8W3HX2ymoAYVdZEoYH5Moei42VV+aW9YOn3iWnwUxWVv6cj+fKCQpU/Px PEUxmiMYJg7uXGnTPSZ2EfiPT2gljoi8uesibwszpzi7tmWR5iYzk/McxsyNpzqO moMFYaGZlv7B/c0OQogpgZTWF1SkpVJQLqq5u9euRQVLLTJIXABzGDRvZSo6CDeX sk+CQ6TcTw3bj+5XNZ0S2fhJeV6L2gwd0yKnGD+ouMXpB+VnUB2Ym/Ux9eocsIWZ NkrWczhfwvtrDxMvarMeYbn0KZm9Ua54+LdQSsBxi8TU01Y++tNtwVjThtd/DbRt EXw6x0PtTTvsp/tAZI3vY4V9pER1i5sPDwXE1OmiMTnDtCQ1D05n5wFm+ug9oBQS gnnihdowdt22JEFOVn+iYTNXiztRMo4TvJHPxTF7MV8z91mSVrBlc69uOSbjBjDz v2hre+/a8ZqbGkv642efzZSRBl8mjcgWGhH7j9njvm3cxskvduiqEwMm+wZ4Fm78 /slav8oC0cGBbTAQrLNxkBCfLESabDKhdDvFUjDp0miMAJCEVMNzsjSOPEEtw7cA WdwdrddA+iejQulBBG5NqNCl2niGOIOj+xcPuhmU/SGo3yJ4PBI= =DjQ2 -----END PGP SIGNATURE----- --8WI4CJN/1CmqA8yt--