[RFC PATCH 0/6] spi: Add OSPI PHY calibration support for spi-cadence-quadspi

[Pratyush Yadav <p.yadav@xxxxxx>]

Hi,

This series adds support for OSPI PHY calibration on the Cadence OSPI
controller. This calibration procedure is needed to allow high clock
speeds in 8D-8D-8D mode. The procedure reads some pre-determined pattern
data from the flash and runs a sequence of test reads to find out the
optimal delays for high speed transfer. More details on the calibration
procedure in patch 5/6.

The main problem here is telling the controller where to find the
pattern and how to read it. This RFC uses nvmem cells which point to a
fixed partition containing the data to do the reads. It depends on [0]
and [1].

The obvious problem with this is it won't work when the partitions are
defined via command line. I don't see any good way to add nvmem cells to
command line partitions. I would like some help or ideas here. We don't
necessarily have to use nvmem either. Any way that can cleanly and
consistently let the controller find out where the pattern is stored is
good.

The dts patch depends on [2].

Tested on TI's J721E EVM.

[0] https://patchwork.ozlabs.org/project/linux-mtd/patch/20210302190012.1255-1-zajec5@xxxxxxxxx/
[1] https://patchwork.ozlabs.org/project/linux-mtd/patch/20210308011853.19360-1-ansuelsmth@xxxxxxxxx/
[2] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20210305153926.3479-2-p.yadav@xxxxxx/

Pratyush Yadav (6):
  spi: spi-mem: Tell controller when device is ready for calibration
  mtd: spi-nor: core: consolidate read op creation
  mtd: spi-nor: core: run calibration when initialization is done
  spi: cadence-qspi: Use PHY for DAC reads if possible
  spi: cadence-qspi: Tune PHY to allow running at higher frequencies
  arm64: dts: ti: k3-j721e-som-p0: Enable PHY calibration

 arch/arm64/boot/dts/ti/k3-j721e-som-p0.dtsi |  55 ++
 drivers/mtd/spi-nor/core.c                  |  74 +-
 drivers/spi/spi-cadence-quadspi.c           | 820 +++++++++++++++++++-
 drivers/spi/spi-mem.c                       |  12 +
 include/linux/spi/spi-mem.h                 |   8 +
 5 files changed, 916 insertions(+), 53 deletions(-)

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2.30.0