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Date: Thu, 13 Jun 2019 15:14:28 +0300
From: Dmitry Osipenko <digetx@...il.com>
To: Peter De Schrijver <pdeschrijver@...dia.com>
Cc: Rob Herring <robh+dt@...nel.org>,
Michael Turquette <mturquette@...libre.com>,
Joseph Lo <josephl@...dia.com>,
Thierry Reding <thierry.reding@...il.com>,
Jonathan Hunter <jonathanh@...dia.com>,
Prashant Gaikwad <pgaikwad@...dia.com>,
devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/8] clk: tegra20/30: Add custom EMC clock
implementation
13.06.2019 13:49, Peter De Schrijver пишет:
> On Fri, May 24, 2019 at 08:23:46PM +0300, Dmitry Osipenko wrote:
>> A proper External Memory Controller clock rounding and parent selection
>> functionality is required by the EMC drivers. It is not available using
>> the generic clock implementation, hence add a custom one. The clock rate
>> rounding shall be done by the EMC drivers because they have information
>> about available memory timings, so the drivers will have to register a
>> callback that will round the requested rate. EMC clock users won't be able
>> to request EMC clock by getting -EPROBE_DEFER until EMC driver is probed
>> and the callback is set up. The functionality is somewhat similar to the
>> clk-emc.c which serves Tegra124+ SoC's, the later HW generations support
>> more parent clock sources and the HW configuration and integration with
>> the EMC drivers differs a tad from the older gens, hence it's not really
>> worth to try to squash everything into a single source file.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>> drivers/clk/tegra/Makefile | 2 +
>> drivers/clk/tegra/clk-tegra20-emc.c | 299 ++++++++++++++++++++++++++++
>> drivers/clk/tegra/clk-tegra20.c | 55 ++---
>> drivers/clk/tegra/clk-tegra30.c | 38 +++-
>> drivers/clk/tegra/clk.h | 6 +
>> include/linux/clk/tegra.h | 14 ++
>> 6 files changed, 362 insertions(+), 52 deletions(-)
>> create mode 100644 drivers/clk/tegra/clk-tegra20-emc.c
>>
>> diff --git a/drivers/clk/tegra/Makefile b/drivers/clk/tegra/Makefile
>> index 4812e45c2214..df966ca06788 100644
>> --- a/drivers/clk/tegra/Makefile
>> +++ b/drivers/clk/tegra/Makefile
>> @@ -17,7 +17,9 @@ obj-y += clk-tegra-fixed.o
>> obj-y += clk-tegra-super-gen4.o
>> obj-$(CONFIG_TEGRA_CLK_EMC) += clk-emc.o
>> obj-$(CONFIG_ARCH_TEGRA_2x_SOC) += clk-tegra20.o
>> +obj-$(CONFIG_ARCH_TEGRA_2x_SOC) += clk-tegra20-emc.o
>> obj-$(CONFIG_ARCH_TEGRA_3x_SOC) += clk-tegra30.o
>> +obj-$(CONFIG_ARCH_TEGRA_3x_SOC) += clk-tegra20-emc.o
>> obj-$(CONFIG_ARCH_TEGRA_114_SOC) += clk-tegra114.o
>> obj-$(CONFIG_ARCH_TEGRA_124_SOC) += clk-tegra124.o
>> obj-$(CONFIG_TEGRA_CLK_DFLL) += clk-tegra124-dfll-fcpu.o
>> diff --git a/drivers/clk/tegra/clk-tegra20-emc.c b/drivers/clk/tegra/clk-tegra20-emc.c
>> new file mode 100644
>> index 000000000000..d971b5425ce3
>> --- /dev/null
>> +++ b/drivers/clk/tegra/clk-tegra20-emc.c
>> @@ -0,0 +1,299 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +#include <linux/bits.h>
>> +#include <linux/clk-provider.h>
>> +#include <linux/clk/tegra.h>
>> +#include <linux/err.h>
>> +#include <linux/io.h>
>> +#include <linux/kernel.h>
>> +#include <linux/slab.h>
>> +
>> +#include "clk.h"
>> +
>> +#define CLK_SOURCE_EMC_2X_CLK_DIVISOR_MASK GENMASK(7, 0)
>> +#define CLK_SOURCE_EMC_2X_CLK_SRC_MASK GENMASK(31, 30)
>> +#define CLK_SOURCE_EMC_2X_CLK_SRC_SHIFT 30
>> +
>> +#define MC_EMC_SAME_FREQ BIT(16)
>> +#define USE_PLLM_UD BIT(29)
>> +
>> +#define EMC_SRC_PLL_M 0
>> +#define EMC_SRC_PLL_C 1
>> +#define EMC_SRC_PLL_P 2
>> +#define EMC_SRC_CLK_M 3
>> +
>> +static const char * const emc_parent_clk_names[] = {
>> + "pll_m", "pll_c", "pll_p", "clk_m",
>> +};
>> +
>> +struct tegra_clk_emc {
>> + struct clk_hw hw;
>> + void __iomem *reg;
>> + bool mc_same_freq;
>> + bool want_low_jitter;
>> +
>> + tegra20_clk_emc_round_cb *round_cb;
>> + void *cb_arg;
>> +};
>> +
>> +static inline struct tegra_clk_emc *to_tegra_clk_emc(struct clk_hw *hw)
>> +{
>> + return container_of(hw, struct tegra_clk_emc, hw);
>> +}
>> +
>> +static unsigned long emc_recalc_rate(struct clk_hw *hw,
>> + unsigned long parent_rate)
>> +{
>> + struct tegra_clk_emc *emc = to_tegra_clk_emc(hw);
>> + u32 val, div;
>> +
>> + val = readl_relaxed(emc->reg);
>> + div = val & CLK_SOURCE_EMC_2X_CLK_DIVISOR_MASK;
>> +
>> + return DIV_ROUND_UP(parent_rate * 2, div + 2);
>> +}
>> +
>> +static u8 emc_get_parent(struct clk_hw *hw)
>> +{
>> + struct tegra_clk_emc *emc = to_tegra_clk_emc(hw);
>> +
>> + return readl_relaxed(emc->reg) >> CLK_SOURCE_EMC_2X_CLK_SRC_SHIFT;
>> +}
>> +
>> +static int emc_set_parent(struct clk_hw *hw, u8 index)
>> +{
>> + struct tegra_clk_emc *emc = to_tegra_clk_emc(hw);
>> + u32 val, div;
>> +
>> + val = readl_relaxed(emc->reg);
>> + val &= ~CLK_SOURCE_EMC_2X_CLK_SRC_MASK;
>> + val |= index << CLK_SOURCE_EMC_2X_CLK_SRC_SHIFT;
>> +
>> + div = val & CLK_SOURCE_EMC_2X_CLK_DIVISOR_MASK;
>> +
>> + if (index == EMC_SRC_PLL_M && div == 0 && emc->want_low_jitter)
>> + val |= USE_PLLM_UD;
>> + else
>> + val &= ~USE_PLLM_UD;
>> +
>> + if (emc->mc_same_freq)
>> + val |= MC_EMC_SAME_FREQ;
>> + else
>> + val &= ~MC_EMC_SAME_FREQ;
>> +
>> + writel_relaxed(val, emc->reg);
>> +
>
> I think technically you need a fence_udelay(1) here, but in practice
> this is probably not needed because you will poll some EMC register for
> the frequency completion anyway. Maybe add a comment about this?
>
>> + return 0;
>> +}
>> +
>> +static int emc_set_rate(struct clk_hw *hw, unsigned long rate,
>> + unsigned long parent_rate)
>> +{
>> + struct tegra_clk_emc *emc = to_tegra_clk_emc(hw);
>> + unsigned int index;
>> + u32 val, div;
>> +
>> + div = div_frac_get(rate, parent_rate, 8, 1, 0);
>> +
>> + val = readl_relaxed(emc->reg);
>> + val &= ~CLK_SOURCE_EMC_2X_CLK_DIVISOR_MASK;
>> + val |= div;
>> +
>> + index = val >> CLK_SOURCE_EMC_2X_CLK_SRC_SHIFT;
>> +
>> + if (index == EMC_SRC_PLL_M && div == 0 && emc->want_low_jitter)
>> + val |= USE_PLLM_UD;
>> + else
>> + val &= ~USE_PLLM_UD;
>> +
>> + if (emc->mc_same_freq)
>> + val |= MC_EMC_SAME_FREQ;
>> + else
>> + val &= ~MC_EMC_SAME_FREQ;
>> +
>> + writel_relaxed(val, emc->reg);
>> +
>
> Same here.
>
>> + return 0;
>> +}
>> +
>> +static int emc_set_rate_and_parent(struct clk_hw *hw,
>> + unsigned long rate,
>> + unsigned long parent_rate,
>> + u8 index)
>> +{
>> + struct tegra_clk_emc *emc = to_tegra_clk_emc(hw);
>> + u32 val, div;
>> +
>> + div = div_frac_get(rate, parent_rate, 8, 1, 0);
>> +
>> + val = readl_relaxed(emc->reg);
>> +
>> + val &= ~CLK_SOURCE_EMC_2X_CLK_SRC_MASK;
>> + val |= index << CLK_SOURCE_EMC_2X_CLK_SRC_SHIFT;
>> +
>> + val &= ~CLK_SOURCE_EMC_2X_CLK_DIVISOR_MASK;
>> + val |= div;
>> +
>> + if (index == EMC_SRC_PLL_M && div == 0 && emc->want_low_jitter)
>> + val |= USE_PLLM_UD;
>> + else
>> + val &= ~USE_PLLM_UD;
>> +
>> + if (emc->mc_same_freq)
>> + val |= MC_EMC_SAME_FREQ;
>> + else
>> + val &= ~MC_EMC_SAME_FREQ;
>> +
>> + writel_relaxed(val, emc->reg);
>> +
>
> And here.
>
>> + return 0;
>> +}
>
> Peter.
>
Thank you very much for the feedback! Indeed, it will be a bit more
robust to add fence_udelay() since one microsecond is practically
nothing and then it will be a part of the clk-change awaiting anyway
(note that EMC driver waits for the interrupt event and doesn't poll the
status), we also don't really care about the EMC rate-change performance
much because it won't happen frequently.
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