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

Nicolas Ferre [off-list ref] writes:

Le 27/01/2016 16:53, Måns Rullgård a écrit :

quoted

Nicolas Ferre [off-list ref] writes:

quoted

Le 05/01/2016 22:50, Måns Rullgård a écrit :

quoted

Cyrille Pitchen [off-list ref] writes:

quoted

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 <redacted>
---
 drivers/spi/spi-atmel.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

[...]

quoted

@@ -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.

Ok, thanks: we thought that AVR32 didn't have a v2 IP: obviously it has.
So yes, I extract the patch by Cyrille to correct this and send it right
now.

If you can test it, it's even better ;-)

I saw the patch, will test it later.

-- 
Måns Rullgård
--
To unsubscribe from this list: send the line "unsubscribe linux-spi" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html