Blackfin: document SPI CS limitations with CPHA=0 (3322c7bb) · Commits · 戴 / test

With the Blackfin on-chip SPI peripheral, there is some logic tied to the CPHA bit whether the Slave Select Line is controlled by hardware (CPHA=0) or controlled by software (CPHA=1). However, the Linux SPI bus driver assumes that the Slave Select being asserted during the entire SPI transfer. So explain these small details for people who need certain SPI modes with standard CS behavior. Signed-off-by:

Michael Hennerich <michael.hennerich@analog.com> Signed-off-by:

Mike Frysinger <vapier@gentoo.org>

Documentation/blackfin/00-INDEX

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Original line number	Diff line number	Diff line
		00-INDEX
		- This file

		bfin-gpio-note.txt
		bfin-gpio-notes.txt
		- Notes in developing/using bfin-gpio driver.

		bfin-spi-notes.txt
		- Notes for using bfin spi bus driver.

Documentation/blackfin/bfin-spi-notes.txt

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Original line number	Diff line number	Diff line
		SPI Chip Select behavior:

		With the Blackfin on-chip SPI peripheral, there is some logic tied to the CPHA
		bit whether the Slave Select Line is controlled by hardware (CPHA=0) or
		controlled by software (CPHA=1). However, the Linux SPI bus driver assumes that
		the Slave Select is always under software control and being asserted during
		the entire SPI transfer. - And not just bits_per_word duration.

		In most cases you can utilize SPI MODE_3 instead of MODE_0 to work-around this
		behavior. If your SPI slave device in question requires SPI MODE_0 or MODE_2
		timing, you can utilize the GPIO controlled SPI Slave Select option instead.

		You can even use the same pin whose peripheral role is a SSEL,
		but use it as a GPIO instead.

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