linux-kernel - Re: [PATCH v4 11/13] clk: tegra: Add EMC clock driver

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Date:	Thu, 13 Nov 2014 11:51:43 +0100
From:	Nikolaus Schulz <nikolaus.schulz@...onic-design.de>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	linux-tegra@...r.kernel.org,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	mikko.perttunen@...si.fi, acourbot@...dia.com,
	Mikko Perttunen <mperttunen@...dia.com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 11/13] clk: tegra: Add EMC clock driver

On Wed, Nov 12, 2014 at 08:56:34AM +0100, Tomeu Vizoso wrote:
> From: Mikko Perttunen <mperttunen@...dia.com>
> 
> The driver is currently only tested on Tegra124 Jetson TK1, but should
> work with other Tegra124 boards, provided that correct EMC tables are
> provided through the device tree. Older chip models have differing
> timing change sequences, so they are not currently supported.
> 
> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
[...]
> diff --git a/drivers/clk/tegra/clk-emc.c b/drivers/clk/tegra/clk-emc.c
> new file mode 100644
> index 0000000..75beacd
> --- /dev/null
> +++ b/drivers/clk/tegra/clk-emc.c
[...]
> +/*
> + * Rounds up unless no higher rate exists, in which case down. This way is
> + * safer since things have EMC rate floors. Also don't touch parent_rate
> + * since we don't want the CCF to play with our parent clocks.
> + */
> +static long emc_round_rate(struct clk_hw *hw, unsigned long rate,
> +		    unsigned long *parent_rate)
> +{
> +	struct tegra_emc *tegra = container_of(hw, struct tegra_emc, hw);
> +	u8 ram_code = tegra_read_ram_code();
> +	struct emc_timing *timing;
> +	int i;
> +
> +	/*
> +	 * Returning the original rate will lead to a more sensible error
> +	 * message when emc_set_rate fails.
> +	 */
> +	if (tegra->num_timings == 0)
> +		return rate;
> +
> +	for (i = 0; i < tegra->num_timings; ++i) {
> +		timing = tegra->timings + i;
> +		if (timing->ram_code != ram_code)
> +			continue;

Is timing->ram_code != ram_code really something that is allowed?

> +
> +		if (timing->rate >= rate)
> +			return timing->rate;
> +	}
> +
> +	return tegra->timings[tegra->num_timings - 1].rate;

If tegra->timings has timings for different ram_codes, the last timing
might not be for the requested ram_code.

> +}
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