linux-kernel - Re: [PATCH v3 2/3] clocksource: Add NPS400 timers driver

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Message-ID: <56B8A482.8040302@linaro.org>
Date:	Mon, 8 Feb 2016 15:21:54 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Noam Camus <noamc@...hip.com>, linux-kernel@...r.kernel.org
Cc:	linux-snps-arc@...ts.infradead.org, marc.zyngier@....com,
	cmetcalf@...hip.com, talz@...hip.com, giladb@...hip.com,
	Rob Herring <robh+dt@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH v3 2/3] clocksource: Add NPS400 timers driver

On 02/06/2016 05:16 PM, Noam Camus wrote:
> From: Noam Camus <noamc@...hip.com>
>
> Add internal tick generator which is shared by all cores.
> Each cluster of cores view it through dedicated address.
> This is used for SMP system where all CPUs synced by same
> clock source.
>
> Signed-off-by: Noam Camus <noamc@...hip.com>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: John Stultz <john.stultz@...aro.org>
> Acked-by: Vineet Gupta <vgupta@...opsys.com>
> ---

[ ... ]

> +static cycle_t nps_clksrc_read(struct clocksource *clksrc)
> +{
> +	int cluster = raw_smp_processor_id() >> NPS_CLUSTER_OFFSET;
> +
> +	return (cycle_t)ioread32be(nps_msu_reg_low_addr[cluster]);
> +}
> +
> +static struct clocksource nps_counter = {
> +	.name	= "EZnps-tick",
> +	.rating = 301,
> +	.read   = nps_clksrc_read,
> +	.mask   = CLOCKSOURCE_MASK(32),
> +	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
> +};
> +
> +static void __init nps_setup_clocksource(struct device_node *node,
> +					 struct clk *clk)
> +{
> +	struct clocksource *clksrc = &nps_counter;
> +	int ret, cluster;
> +
> +	for (cluster = 0; cluster < NPS_CLUSTER_NUM; cluster++)
> +		nps_msu_reg_low_addr[cluster] =
> +			nps_host_reg((cluster << NPS_CLUSTER_OFFSET),
> +				 NPS_MSU_BLKID, NPS_MSU_TICK_LOW);
> +
> +	ret = clk_prepare_enable(clk);
> +	if (ret)
> +		pr_err("Couldn't enable parent clock\n");
> +
> +	nps_timer_rate = clk_get_rate(clk);

If there is an error, you continue the execution of the code. I guess 
you expect the system to hang in any case with the error in the console, 
right ?

> +	ret = clocksource_register_hz(clksrc, nps_timer_rate);

You can simplify the driver even more by using clocksource_mmio_init.

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