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

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Date:	Wed, 27 Jan 2016 16:46:51 +0100
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Måns Rullgård <mans@...sr.com>
CC:	Cyrille Pitchen <cyrille.pitchen@...el.com>,
	Mark Browk <broonie@...nel.org>, <linux-spi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"Yang, Wenyou" <Wenyou.Yang@...el.com>
Subject: Re: [PATCH v3 1/3] spi: atmel: add support for the internal
 chip-select of the spi controller

Le 05/01/2016 22:50, Måns Rullgård a écrit :
> Cyrille Pitchen <cyrille.pitchen@...el.com> 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@...el.com>
>> ---
>>  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.

Bye,
-- 
Nicolas Ferre