tree d738bb500deb3d05f467c8cc59b347e79f49e546
parent fd9571a8d7707ddea536456bc6e69551689bdf7b
author Sean Anderson <seanga2@gmail.com> 1602889071 -0400
committer Jagan Teki <jagan@amarulasolutions.com> 1608288397 +0530

spi: dw: Add support for multiple CTRLR0 layouts

CTRLR0 can have several different layouts depending on the specific device
(dw-apb-ssi vs dwc-ssi), and specific parameters set during synthesis.
Update the driver to support three specific configurations: dw-apb-ssi with
SSI_MAX_XFER_SIZE=16, dw-apb-ssi with SSI_MAX_XFER_SIZE=32, and dwc-ssi.

dw-apb-ssi is the version of the device on Altera/Intel SoCFPGAs, MSCC
SoCs, and Canaan Kendryte K210 SoCs. This is the only version this driver
supported before this change. The register layout before version 3.23a is:

|   31 .. 16  |
| other stuff |

|   15 .. 10  | 9 .. 8 | 7 .. 6 | 5 .. 4 | 3 .. 0 |
| other stuff |  TMOD  |  MODE  |  FRF   |  DFS   |

Note that DFS (Data Frame Size) is only 4 bits, limiting transfers to data
frames of 16 bits or less.

In version 3.23a, the SSI_MAX_XFER_SIZE parameter was introduced. This
parameter defaults to 16 (resulting in the same layout as prior versions),
but may also be set to 32. To allow setting longer data frame sizes, a new
DFS_32 register was introduced:

|   31 .. 21  | 20 .. 16 |
| other stuff |  DFS_32  |

|   15 .. 10  | 9 .. 8 | 7 .. 6 | 5 .. 4 |  3 .. 0   |
| other stuff |  TMOD  |  MODE  |  FRF   | all zeros |

The old DFS field no longer controls the data frame size. To detect this
layout, we try writing 0xF to DFS. If we read back 0x0, then this device
has SSI_MAX_XFER_SIZE=32.

dwc-ssi is the version of the device on Intel Keem Bay SoCs and Canaan
Kendryte K210 SoCs. The layout of ctrlr0 is:

|   31 .. 16  |
| other stuff |

|   15 .. 12  | 11 .. 10 | 9 .. 8 | 7 .. 6 | 4 .. 0 |
| other stuff |   TMOD   |  MODE  |  FRF   | DFS_32 |

The semantics of the fields have not changed since the previous version.
However, SSI_MAX_XFER_SIZE is effectively always 32.

To support these different layouts, we model our approach on the one
which the Linux kernel has taken. During probe, the driver calls an init
function stored in driver_data. This init function is responsible for
determining the layout of CTRLR0, and supplying the update_cr0 function.

The style of and information behind this commit is based on the Linux MMIO
driver for these devices. Specific reference was made to the series adding
support for Intel Keem Bay SoCs [1].

[1] https://lore.kernel.org/linux-spi/20200505130618.554-1-wan.ahmad.zainie.wan.mohamad@intel.com/

Signed-off-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>