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

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Message-ID: <yw1xfuxjj6zm.fsf@unicorn.mansr.com>
Date:	Wed, 27 Jan 2016 16:57:01 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	Cyrille Pitchen <cyrille.pitchen@...el.com>,
	Mark Brown <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

Nicolas Ferre <nicolas.ferre@...el.com> writes:

> Le 27/01/2016 16:53, Måns Rullgård a écrit :
>> Nicolas Ferre <nicolas.ferre@...el.com> writes:
>> 
>>> 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.
>> 
>> 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