Re: [PATCH v5 12/14] clk: tegra: Add EMC clock driver

Nikolaus Schulz
2014-11-19T15:28:53Z

On Tue, Nov 18, 2014 at 01:13:14PM +0100, Tomeu Vizoso wrote:
> From: Mikko Perttunen <mperttunen@nvidia.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@nvidia.com>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
>
> ---
>
> v5: * Get a pointer to the EMC driver at runtime, to be used when
> calling the EMC API.
> * Misc. style fixes
> * Fix logic for rounding down to a high rate
>
> v4: * Adapt to changes in the OF bindings
> * Improve error handling
> * Fix comment style
> * Make static a few more functions
>
> v3: * Add some locking to protect the registers that are shared with the MC
> clock
>
> v2: * Make sure that the clock is properly registered
> * Bail out early from attempts to set the same rate
> ---
> diff --git a/drivers/clk/tegra/clk-emc.c b/drivers/clk/tegra/clk-emc.c
> new file mode 100644
> index 0000000..399d945
> --- /dev/null
> +++ b/drivers/clk/tegra/clk-emc.c
> @@ -0,0 +1,532 @@
> +/*
> + * 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_clk_emc *tegra;
> + u8 ram_code = tegra_read_ram_code();
> + struct emc_timing *timing;
> + int i;
> +
> + tegra = container_of(hw, struct tegra_clk_emc, hw);
> +
> + for (i = 0; i < tegra->num_timings; i++) {
> + timing = tegra->timings + i;
> + if (timing->ram_code != ram_code)
> + continue;
> +
> + if (timing->rate >= rate)
> + return timing->rate;
> + }
> +
> + for (i = tegra->num_timings - 1; i >= 0; i--) {
> + timing = tegra->timings + i;
> + if (timing->ram_code != ram_code)
> + continue;
> +
> + return timing->rate;
> + }

While this is technically not wrong, it could be simplified to something
like

struct emc_timing *timing = NULL;

for (i = 0; i < tegra->num_timings; i++) {
if (tegra->timings[i].ram_code != ram_code)
continue;
timing = tegra->timings + i;
if (timing->rate >= rate)
return timing->rate;
}
if (timing)
return timing->rate;

> +
> + return __clk_get_rate(hw->clk);
> +}