linux-kernel - Re: [PATCH v3] spi: dts: sun4i: Add support for hardware-based wait time between words

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Message-ID: <CAGNoLaOckrgv5NP6eTOt8shj5f069DKFrxx+8afydqcAZH5HMw@mail.gmail.com>
Date:	Mon, 14 Dec 2015 08:31:55 +0100
From:	Marcus Weseloh <mweseloh42@...il.com>
To:	Rob Herring <robh@...nel.org>
Cc:	linux-sunxi <linux-sunxi@...glegroups.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Brown <broonie@...nel.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	"Mailing List, Arm" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] spi: dts: sun4i: Add support for hardware-based wait
 time between words

Hi,

2015-12-14 2:29 GMT+01:00 Rob Herring <robh@...nel.org>:
> On Mon, Dec 14, 2015 at 12:04:11AM +0100, Marcus Weseloh wrote:
>> Adds a new property "spi-word-wait-ns" to the spi-bus binding that allows
[...]
>> diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
>> index bbaa857..2d6034f 100644
>> --- a/Documentation/devicetree/bindings/spi/spi-bus.txt
>> +++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
>> @@ -61,6 +61,8 @@ contain the following properties.
>>                        used for MOSI. Defaults to 1 if not present.
>>  - spi-rx-bus-width - (optional) The bus width(number of data wires) that
>>                        used for MISO. Defaults to 1 if not present.
>> +- spi-word-wait-ns - (optional) Hardware based delay between transmission of
>> +                      words in nanoseconds
>
> Could be a software delay if the h/w doesn't support delays.

Of course, I was still trapped in my sun4i specific thinking. Will
remove the hardware reference.

[...]
>> +     /* Setup wait time between words */
>> +     of_property_read_u32(spi->dev.of_node, "spi-word-wait-ns",
>> +                          &wait_ns);
>
> Read this in probe and save the value rather than fetching every
> transfer.

But this is a slave property I'm using here. If I read and store it in
probe in the spi-sun4i driver, I won't have access to the slave node
property, will I?

Cheers,

    Marcus
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