[PATCH v4 00/16] spi: cadence-quadspi: add PHY tuning support

[Santhosh Kumar K <s-k6@ti.com>]

This series implements PHY tuning support for the Cadence QSPI controller
to enable reliable high-speed operations. Without PHY tuning, controllers
use conservative timing that limits performance. PHY tuning calibrates
RX/TX delay lines to find optimal data capture timing windows, enabling
operation up to the controller's maximum frequency.

Background:
High-speed SPI memory controllers require precise timing calibration for
reliable operation. At higher frequencies, board-to-board variations make
fixed timing parameters inadequate. The Cadence QSPI controller includes
a PHY interface with programmable delay lines (0-127 taps) for RX and TX
paths, but these require runtime calibration to find the valid timing
window.

Approach:
Add SDR/DDR PHY tuning algorithms for the Cadence controller:

SDR Mode Tuning (1D search):
 - Searches for two consecutive valid RX delay windows
 - Selects the larger window and uses its midpoint for maximum margin
 - TX delay fixed at maximum (127) as it's less critical in SDR

DDR Mode Tuning (2D search):
 - Finds RX boundaries (rxlow/rxhigh) using TX window sweeps
 - Finds TX boundaries (txlow/txhigh) at fixed RX positions
 - Defines valid region corners and detects gaps via binary search
 - Applies temperature compensation for optimal point selection
 - Handles single or dual passing regions with different strategies

Patch description:
Infrastructure (1-5):
 - Patch 1:   Add spi-max-post-config-frequency to describe maximum
              frequency achievable post controller configuration
 - Patch 2:   Add spi-phy-pattern-partition phandle for
              NOR flash PHY tuning pattern location
 - Patch 3:   Parse spi-max-post-config-frequency in spi.c; adds
              spi_device.post_config_max_speed_hz (0 when not set
              keeping all existing DT fully compatible)
 - Patch 4:   Extend spi_mem_adjust_op_freq() with a bypass: if
              op->max_freq equals post_config_max_speed_hz, return
              immediately leaving op->max_freq unchanged. All other
              ops are capped to max_speed_hz
 - Patch 5:   Add execute_tuning callback to spi_controller_mem_ops and
              spi_mem_execute_tuning() wrapper in SPI-MEM core

Cadence QSPI Implementation (6-12):
 - Patch 6:   Move cqspi_readdata_capture() earlier (preparatory)
 - Patch 7:   Add DQS bit to cqspi_readdata_capture() (preparatory)
 - Patch 8:   Add complete PHY tuning support: DLL management, pattern
              verification (NOR via spi-phy-pattern-partition phandle,
              NAND via write-to-cache), SDR 1D and DDR 2D search
              algorithms with temperature compensation, AM654-specific
              execute_tuning entry point;
 - Patch 9:   Reject 2-byte-address DDR operations via a new
              CQSPI_NO_2BYTE_ADDR_PHY_DDR quirk flag to work around
              AM654 OSPI erratum i2383
 - Patch 10:  Refactor direct read path for PHY support (preparatory)
 - Patch 11:  Enable PHY for direct reads, split the transfer into an
              unaligned head, a 16-byte-aligned middle section with PHY
              active, and an unaligned tail
 - Patch 12:  Enable PHY for indirect writes of at least                        
              CQSPI_PHY_MIN_INDIRECT_WRITE_LEN bytes

MTD core (13-16):
 - Patch 13:  Extract spinand_select_op_variant() into a shared helper
              spinand_op_find_best() with a skip_mask
 - Patch 14:  Negotiate optimal PHY operating point before dirmap
              creation
 - Patch 15:  Extract spi_nor_spimem_get_read_op() helper (preparatory)
 - Patch 16:  Execute PHY tuning in spi_nor_probe() before creating
              dirmaps

Testing:
This series was tested on TI's
AM62Ax SK with OSPI NAND flash and
AM62Px SK with OSPI NOR flash:

Read throughput:
|----------------------------------------|
|                | non-PHY   | PHY       |
|----------------------------------------|
| OSPI NOR (8D)  | 37.5 MB/s | 216 MB/s  |
|----------------------------------------|
| OSPI NAND (8S) | 9.2 MB/s  | 35.1 MB/s |
|----------------------------------------|

Write throughput:
|----------------------------------------|
|                | non-PHY   | PHY       |
|----------------------------------------|
| OSPI NAND (8S) | 6 MB/s    | 9.2 MB/s  |
|----------------------------------------|

Test log: https://gist.github.com/santhosh21/fe98754e52970287eb9011154100b62d
Repo: https://github.com/santhosh21/linux/commits/phy_tuning_v4/

Changes in v4:
 - Add spi-max-post-config-frequency instead of extending spi-max-frequency
   to accept an optional second value
 - Replace spi_mem_apply_base_freq_cap() with spi_mem_adjust_op_freq() extension
 - For SPI NOR/NAND, execute PHY tuning before the dirmap creation
 - For SPI NAND, execute PHY tuning across all operation variants available,
   perform duration comparison, and select the best resulting variant
   by taking controller-specific restrictions into account
 - Move i2383 check from cqspi_supports_mem_op() to cqspi_am654_ospi_execute_tuning()
 - Rename cdns,phy-pattern-partition to spi-phy-pattern-partition,
   cqspi_phy_enable to cqspi_tune_phy and f_pdata->use_phy to use_tuned_phy
 - Remove redundant spi-max-frequency parsing in driver cqspi_of_get_flash_pdata()
 - Extract DMA refactoring into a preparatory patch
 - Rebase on v7.1
 - Collect tags from Miquel
 - Link to v3: https://lore.kernel.org/linux-spi/20260527175527.2247679-1-s-k6@ti.com/

Changes in v3:
 - Drop spi-has-dqs DT property; DQS is now enabled automatically when
   the selected read operation uses DDR signalling (dtr flags in the op)
 - Extend spi-max-frequency to accept an optional second value forming a
   [base-freq, max-freq] pair; the presence of two values signals PHY
   tuning intent and encodes both the conservative base speed and the
   calibration target in one property
 - Add base_speed_hz to struct spi_device (spi.c/spi.h) and parse the
   two-element array there; single-value DT is fully backward-compatible
 - Move frequency enforcement from the cadence driver to core: new
   spi_mem_apply_base_freq_cap() called from spi_mem_exec_op() replaces
   the per-driver cqspi_op_matches_tuned() and non_phy_clk_rate field
 - Propagate the tuned max_freq to dirmap op templates after
   execute_tuning() succeeds; store persistent op templates in
   spi_nor.max_read_op and spinand.{max_read,max_write}_op so the
   frequency writeback survives across the probe call
 - Replace NOR pattern partition lookup by name with a
   cdns,phy-pattern-partition DT phandle pointing directly to the
   partition node
 - Add CQSPI_NO_2BYTE_ADDR_PHY_DDR quirk and reject 2-byte-address DDR
   ops in cqspi_supports_mem_op() to work around AM654 erratum i2383
 - Remove RFC tag
 - Rebase on v7.1-rc5
 - Collect tags from Miquel
 - Link to v2: https://lore.kernel.org/linux-spi/20260113141617.1905039-1-s-k6@ti.com/

Changes in v2:
 - Restructure the .execute_tuning() call from spi-mem clients instead
   of mtdcore with best read_op and write_op (optional) passed
 - Add compatible-specific .execute_tuning() call which can be called by
   spi_mem_execute_tuning() if exists
 - Handle tuning requirement check by controller instead of spi-mem
   clients
 - Add support to write the phy_pattern to cache if relevant write_op
   is passed or get the partition offset which contains the phy_pattern
 - Add tuning algorithm for DDR mode
 - Add support for DQS
 - Restrict PHY frequency to tuned operations
 - Link to v1: https://lore.kernel.org/linux-spi/20250811193219.731851-1-s-k6@ti.com/

Signed-off-by: Santhosh Kumar K <s-k6@ti.com>

Pratyush Yadav (1):
  mtd: spi-nor: extract read op template construction into helper

Santhosh Kumar K (15):
  spi: dt-bindings: add spi-max-post-config-frequency property
  spi: dt-bindings: add spi-phy-pattern-partition property
  spi: parse spi-max-post-config-frequency into post_config_max_speed_hz
  spi: spi-mem: teach spi_mem_adjust_op_freq() about post-config ops
  spi: spi-mem: add execute_tuning callback and spi_mem_execute_tuning()
  spi: cadence-quadspi: move cqspi_readdata_capture earlier
  spi: cadence-quadspi: add DQS support to read data capture
  spi: cadence-quadspi: add PHY tuning support
  spi: cadence-quadspi: skip DDR PHY tuning for 2-byte-address ops
    (i2383)
  spi: cadence-quadspi: refactor direct read path for PHY support
  spi: cadence-quadspi: enable PHY for direct reads
  spi: cadence-quadspi: enable PHY for indirect writes
  mtd: spinand: extract variant ranking logic into
    spinand_op_find_best()
  mtd: spinand: negotiate optimal PHY operating point before dirmap
    creation
  mtd: spi-nor: run PHY tuning after init and update dirmap frequency

 .../bindings/spi/cdns,qspi-nor.yaml           |   19 +
 .../bindings/spi/spi-peripheral-props.yaml    |   13 +
 drivers/mtd/nand/spi/core.c                   |  246 +-
 drivers/mtd/spi-nor/core.c                    |   80 +-
 drivers/spi/spi-cadence-quadspi.c             | 2265 +++++++++++++++--
 drivers/spi/spi-mem.c                         |   40 +
 drivers/spi/spi.c                             |    2 +
 include/linux/mtd/spi-nor.h                   |    3 +
 include/linux/mtd/spinand.h                   |   11 +
 include/linux/spi/spi-mem.h                   |   14 +
 include/linux/spi/spi.h                       |    3 +
 11 files changed, 2493 insertions(+), 203 deletions(-)

-- 
2.34.1