Re: [PATCH v3 1/3] spi: atmel: add support for the internal chip-select of the spi controller

From: Måns Rullgård
Date: Wed Jan 27 2016 - 10:53:39 EST

Nicolas Ferre <nicolas.ferre@xxxxxxxxx> writes:

> Le 05/01/2016 22:50, Måns Rullgård a écrit :
>> Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx> writes:
>>> This patch relies on the CSAAT (Chip Select Active After Transfer) feature
>>> introduced by the version 2 of the spi controller. This new mode allows to
>>> use properly the internal chip-select output pin of the spi controller
>>> instead of using external gpios. Consequently, the "cs-gpios" device-tree
>>> property becomes optional.
>>> When the new CSAAT bit is set into the Chip Select Register, the internal
>>> chip-select output pin remains asserted till both the following conditions
>>> become true:
>>> - the LASTXFER bit is set into the Control Register (or the Transmit Data
>>> Register)
>>> - the Transmit Data Register and its shift register are empty.
>>> WARNING: if the LASTXFER bit is set into the Control Register then new
>>> data are written into the Transmit Data Register fast enough to keep its
>>> shifter not empty, the chip-select output pin remains asserted. Only when
>>> the shifter becomes empty, the chip-select output pin is unasserted.
>>> When the CSAAT bit is clear in the Chip Select Register, the LASTXFER bit
>>> is ignored in both the Control Register and the Transmit Data Register.
>>> The internal chip-select output pin remains active as long as the Transmit
>>> Data Register or its shift register are not empty.
>>> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx>
>>> ---
>>> drivers/spi/spi-atmel.c | 37 ++++++++++++++++++++++++++++---------
>>> 1 file changed, 28 insertions(+), 9 deletions(-)
>> [...]
>>> @@ -1338,6 +1350,13 @@ static int atmel_spi_probe(struct platform_device *pdev)
>>> atmel_get_caps(as);
>>> + as->use_cs_gpios = true;
>>> + if (atmel_spi_is_v2(as) &&
>>> + !of_get_property(pdev->dev.of_node, "cs-gpios", NULL)) {
>>> + as->use_cs_gpios = false;
>>> + master->num_chipselect = 4;
>>> + }
>> This part breaks the AVR32 boards and probably anything else that
>> doesn't use devicetree but does use GPIOs for chip select.
> Hi Mans,
> I have difficulties finding why you may enter this test. So, maybe you
> can give me a clue by reading for me the value that resides in the SPI
> version register: you can have it by reading at 0xFFE000FC for instance
> (actually the atmel_get_caps() dev_info() call gives it as well in the
> boot log which is somewhat easier: I tried to find one on the Internet
> without success...).
> So I think that just fixing the logic in atmel_get_caps() introduced by
> d4820b7496219edd9a7055022681364d304525f7 can make it come back to a
> situation where the ARV32 was more tested than nowadays.

atmel_spi atmel_spi.0: version: 0x171
atmel_spi atmel_spi.0: Atmel SPI Controller at 0xffe00000 (irq 3)

atmel_spi_is_v2() returns true for version > 0x121.

Måns Rullgård