[PATCH v6 0/3] spi: dts: sun4i: Add support for wait time between word transmissions

Marcus Weseloh
2015-12-26T15:53:19Z

Hi all,

This is the sixth version of the patch set that adds a new property
"spi-word-wait-ns" to the spi-bus binding to allow SPI slave devices to set
a wait time between the transmission of words. It modifies the spi_device
struct and slave device probing to read and store the new property.

Also modifies the sun4i SPI master driver to make use of the new property.
This specific SPI controller needs 3 clock cycles to set up the delay, which
makes the minimum non-zero wait time on this hardware 4 clock cycles.

It now also fixes multiple problems in the sun4i clock calculation:
- The A10/A20 datasheet contains the formula AHB_CLK / (2^(n+1)) to calculate
SPI_CLK from CDR1, but this formula is wrong. The actual formula -
determined by analyzing the actual waveforms on a A20 SoC - is AHB_CLK /
(2^n).

- The divisor calculations for CDR1 and CDR2 both rounded to the nearest
integer. This could lead to a transfer speed that is higher than the
requested speed. This patch changes both calculations to always round down.

- The mclk frequency was only ever increased, never decreased. This could
lead to unpredictable transfer speeds, depending on the order in which
transfers with different speeds where serviced by the SPI driver.

Changes from v1:
* renamed the property for more clarity
* wait time is set in nanoseconds instead of number of clock cycles
* transparently handle the 3 setup clock cycles

Changes from v2:
* fixed typo in comment
* moved parameter to spi-bus binding, dropping the vendor prefix
* changed commit summary and description to reflect the changes

Changes from v3:
* remove reference to "hardware" in comments and description, as the wait
time could also be implemented in software
* read and set property value in spi core

Changes from v4:
* log with dev_dbg instead of dev_info
* split patch into two separate ones for SPI-core and sun4i parts

Changes from v5:
* Add Maxime's Reviewed-by and Rob's Acked-by to the SPI core patch
* Add patch to fix clock calculation
* Use actual SPI speed instead of tfr->speed_hz for wait time calculation

Marcus Weseloh (3):
spi: dts: Add new device property to specifcy a wait time between word
transmissions
spi: sun4i: Fix clock calculations to be predictable and never exceed
the requested rate
spi: sun4i: Add support for wait time between word transmissions

Documentation/devicetree/bindings/spi/spi-bus.txt | 2 +
drivers/spi/spi-sun4i.c | 51 ++++++++++++++++++-----
drivers/spi/spi.c | 2 +
include/linux/spi/spi.h | 2 +
4 files changed, 46 insertions(+), 11 deletions(-)

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1.9.1