commit 859ca18ced83ed3b8b529112da5f214ede3d38b0
author Furquan Shaikh <furquan@google.com> Fri Jan 15 17:12:12 2021 -0800
committer Patrick Georgi <pgeorgi@google.com> Mon Jan 25 08:48:38 2021 +0000
tree 442530c9f30c04b1792731414587852aa76a8c5e
parent 99157c1f4a80556462ca22a4ade87b2c8d09e674

soc/intel/common: Add support for populating meminit data

This change adds support for a common block memory driver that can be
used for performing the required operations to read SPD data for
different memory channel DIMMs. This data can then be used by the SoC
code to populate different memory related UPDs.

Most recent Intel platforms follow a similar pattern for configuring
FSP-M UPDs for initializing memory. These platforms use one of the
following topologies:
1. Memory down
2. DIMM modules
3. Mixed

Thus, SPD data is either obtained from CBFS (for memory down topology)
or from on-module EEPROM (for DIMM modules). This SPD data read from
CBFS or EEPROM is then passed into FSP-M using SPD UPDs for different
channels/DIMMs as per the memory organization.

Similarly, DQ/DQS configuration is accepted from mainboard and passed
into FSP-M using UPDs as per the FSP-M/MRC organization of memory
channels.

Different memory technologies on a platform support physical channels
of different widths. Since the data bus width is fixed for a platform,
the number of physical channels is determined by data bus width /
physical channel width. The number of physical channels are different
depending upon the size of physical channel supported by the memory
technology. FSP-M for a platform uses the same set of UPDs for
different memory technologies and aims at providing maximum
flexibility. Thus, the platform code needs to format mainboard inputs
for DQ, DQS and SPD into the UPDs appropriately as per the memory
technology used by the board.

Example: DDR4 on TGL supports 2 physical channels each 64-bit
wide. However, FSP-M UPDs assume channels 16-bit wide. Thus, FSP-M
provides 16 UPDs for SPDs (considering 2 DIMMs per channel and 8
channels with each channel 16-bit wide). Hence, for DDR4, only the SPD
UPDs for MRC channel 0 and 4 are supposed to be used.

This common driver allows the SoC to define the attributes of the
platform:
1. DIMMS_PER_CHANNEL: Maximum DIMMs that are supported per channel by
any memory technology on the platform
2. DATA_BUS_WIDTH: Width of the data bus.
3. MRC_CHANNEL_WIDTH: Width of the channel as used by the MRC to
define UPDs.

In addition to this, the SoC can define different attributes of each
memory technology supported by the platform using `struct
soc_mem_cfg`:
1. Number of physical channels
2. Physical channel to MRC channel mapping
3. Masks for memory down topologies

Using the above information about different memory technologies
supported by the platform and the mainboard configuration for SPD,
the common block memory driver reads SPD data and provides pointers to
this data for each dimm within each channel back to the SoC code. SoC
code can then use this information to configure FSP-M UPDs
accordingly. In addition to that, the common block driver also returns
information about how the channels are populated so that the SoC code
can use this information to expose DQ/DQS information in FSP-M UPDs.

This driver aims at minimizing the effort required for supporting
different memory technologies on any new Intel SoC by reducing per-SoC
effort to a table of configurations rather than having to implement
similar logic for each SoC.

BUG=b:172978729

Change-Id: I256747f0ffc49fb326cd8bc54a6a7b493af139c0
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49040
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: EricR Lai <ericr_lai@compal.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>