linux-kernel - Re: [PATCH/RFC 4/6] spi: slave: Add SPI slave handler reporting boot up time

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Message-ID: <20160718121427.GS30372@sirena.org.uk>
Date:	Mon, 18 Jul 2016 13:14:27 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Geert Uytterhoeven <geert+renesas@...der.be>
Cc:	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Magnus Damm <magnus.damm@...il.com>,
	Hisashi Nakamura <hisashi.nakamura.ak@...esas.com>,
	Hiromitsu Yamasaki <hiromitsu.yamasaki.ym@...esas.com>,
	linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC 4/6] spi: slave: Add SPI slave handler reporting boot
 up time

On Wed, Jun 22, 2016 at 03:42:07PM +0200, Geert Uytterhoeven wrote:
> Add an SPI slave handler responding with the time of reception of the
> last SPI message.
> 
> This can be used by an external microcontroller as a dead man's switch.

The subject says boot up time, this says time of reception of the last
message.  Which is it?

> +static int spi_slave_time_send(struct spi_device *spi)
> +{
> +	__be32 msg[2];
> +	u32 rem_ns;
> +	u64 ts;
> +
> +	ts = local_clock();
> +	rem_ns = do_div(ts, 1000000000) / 1000;
> +
> +	msg[0] = cpu_to_be32(ts);
> +	msg[1] = cpu_to_be32(rem_ns);
> +
> +	return spi_write(spi, &msg, sizeof(msg));
> +}

Looks like uptime which is a third thing.

> +static int spi_slave_time_remove(struct spi_device *spi)
> +{
> +	struct spi_slave_time_priv *priv = spi_get_drvdata(spi);
> +
> +	/* FIXME Doesn't work, as spi_write() is blocked on a completion */
> +	kthread_stop(priv->thread);

spi_async()?  Still no cancellation on the actual operation but it
pushes it more inside the framework.

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