Date:   Wed, 11 Jul 2018 10:37:08 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Kevin Hilman <khilman@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/3] soc: amlogic: Add Meson GX Clock Measure driver

On 09/07/2018 23:41, Kevin Hilman wrote:
> Martin Blumenstingl <martin.blumenstingl@...glemail.com> writes:
> 
>> Hi Neil,
>>
>> On Wed, Jul 4, 2018 at 10:41 AM Neil Armstrong <narmstrong@...libre.com> wrote:
>>>
>>> Hi Martin,
>>>
>>> On 03/07/2018 21:18, Martin Blumenstingl wrote:
>>>> Hi Neil,
>>>>
>>>> On Tue, Jul 3, 2018 at 3:23 PM Neil Armstrong <narmstrong@...libre.com> wrote:
>>>>>
>>>>> The Amlogic Meson GX SoCs embeds a clock measurer IP to measure the internal
>>>>> clock paths frequencies.
>>>>> The precision is in the order of the MHz.
>>>>>
>>>>> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
>>>>> ---
>>>>>  drivers/soc/amlogic/Kconfig                |   8 ++
>>>>>  drivers/soc/amlogic/Makefile               |   1 +
>>>>>  drivers/soc/amlogic/meson-gx-clk-measure.c | 224 +++++++++++++++++++++++++++++
>>>>>  3 files changed, 233 insertions(+)
>>>>>  create mode 100644 drivers/soc/amlogic/meson-gx-clk-measure.c
>>>>>
>>>>> diff --git a/drivers/soc/amlogic/Kconfig b/drivers/soc/amlogic/Kconfig
>>>>> index b04f6e4..4a3217d 100644
>>>>> --- a/drivers/soc/amlogic/Kconfig
>>>>> +++ b/drivers/soc/amlogic/Kconfig
>>>>> @@ -1,5 +1,13 @@
>>>>>  menu "Amlogic SoC drivers"
>>>>>
>>>>> +config MESON_GX_CLK_MEASURE
>>>>> +       bool "Amlogic Meson GX SoC Clock Measure driver"
>>>>> +       depends on ARCH_MESON || COMPILE_TEST
>>>>> +       default ARCH_MESON
>>>>> +       help
>>>>> +         Say yes to support of Measuring a set of internal SoC clocks
>>>>> +         from the debugfs interface.
>>>>> +
>>>>>  config MESON_GX_SOCINFO
>>>>>         bool "Amlogic Meson GX SoC Information driver"
>>>>>         depends on ARCH_MESON || COMPILE_TEST
>>>>> diff --git a/drivers/soc/amlogic/Makefile b/drivers/soc/amlogic/Makefile
>>>>> index 8fa3218..a0ad966 100644
>>>>> --- a/drivers/soc/amlogic/Makefile
>>>>> +++ b/drivers/soc/amlogic/Makefile
>>>>> @@ -1,3 +1,4 @@
>>>>> +obj-$(CONFIG_MESON_GX_CLK_MEASURE) += meson-gx-clk-measure.o
>>>>>  obj-$(CONFIG_MESON_GX_SOCINFO) += meson-gx-socinfo.o
>>>>>  obj-$(CONFIG_MESON_GX_PM_DOMAINS) += meson-gx-pwrc-vpu.o
>>>>>  obj-$(CONFIG_MESON_MX_SOCINFO) += meson-mx-socinfo.o
>>>>> diff --git a/drivers/soc/amlogic/meson-gx-clk-measure.c b/drivers/soc/amlogic/meson-gx-clk-measure.c
>>>>> new file mode 100644
>>>>> index 0000000..434d9f3
>>>>> --- /dev/null
>>>>> +++ b/drivers/soc/amlogic/meson-gx-clk-measure.c
>>>
>>> [...]
>>>
>>>>> +       CLK_MSR_ID(57, "wave420l_c"),
>>>>> +       CLK_MSR_ID(58, "wave420l_b"),
>>>> AFAIK the Chips&Media WAVE420L video codec is only available on GXM (S912)
>>>> I assume reading this on GXBB or GXL simply reads 0?
>>>
>>> Yes
>>>
>>>>
>>>>> +       CLK_MSR_ID(59, "hcodec"),
>>>>> +       CLK_MSR_ID(60, "alt_32k"),
>>>>> +       CLK_MSR_ID(61, "gpio_msr"),
>>>>> +       CLK_MSR_ID(62, "hevc"),
>>>>> +       CLK_MSR_ID(66, "vid_lock"),
>>>>> +       CLK_MSR_ID(70, "pwm_f"),
>>>>> +       CLK_MSR_ID(71, "pwm_e"),
>>>>> +       CLK_MSR_ID(72, "pwm_d"),
>>>>> +       CLK_MSR_ID(73, "pwm_C"),
>>>> should this be pwm_c (instead of pwm_C)?
>>>>
>>>>> +       CLK_MSR_ID(75, "aoclkx2_int"),
>>>>> +       CLK_MSR_ID(76, "aoclk_int"),
>>>>> +       CLK_MSR_ID(77, "rng_ring_osc_0"),
>>>>> +       CLK_MSR_ID(78, "rng_ring_osc_1"),
>>>>> +       CLK_MSR_ID(79, "rng_ring_osc_2"),
>>>>> +       CLK_MSR_ID(80, "rng_ring_osc_3"),
>>>>> +       CLK_MSR_ID(81, "vapb"),
>>>>> +       CLK_MSR_ID(82, "ge2d"),
>>>>> +};
>>>> I did a quick check whether the clock IDs are really the same for all GX SoCs:
>>>> apart from clocks missing on older SoCs (see for example the WAVE420L
>>>> clocks above) there were only minor renames but no conflicts!
>>>
>>> I did the same work ! I will add this detail to the commit log.
>>> Thanks for checking ;-)
>> :)
>>
>>>>
>>>>> +
>>>>> +static int meson_gx_measure_id(struct meson_gx_msr *priv, unsigned int id)
>>>>> +{
>>>>> +       unsigned int val;
>>>>> +       int ret;
>>>>> +
>>>>> +       regmap_write(priv->regmap, MSR_CLK_REG0, 0);
>>>>> +
>>>>> +       /* Set measurement gate to 50uS */
>>>>> +       regmap_update_bits(priv->regmap, MSR_CLK_REG0, MSR_CLK_DIV,
>>>>> +                          FIELD_PREP(MSR_CLK_DIV, DIV_50US));
>>>>> +
>>>>> +       /* Set ID */
>>>>> +       regmap_update_bits(priv->regmap, MSR_CLK_REG0, MSR_CLK_SRC,
>>>>> +                          FIELD_PREP(MSR_CLK_SRC, id));
>>>>> +
>>>>> +       /* Enable & Start */
>>>>> +       regmap_update_bits(priv->regmap, MSR_CLK_REG0,
>>>>> +                          MSR_RUN | MSR_ENABLE,
>>>>> +                          MSR_RUN | MSR_ENABLE);
>>>>> +
>>>>> +       ret = regmap_read_poll_timeout(priv->regmap, MSR_CLK_REG0,
>>>>> +                                      val, !(val & MSR_BUSY), 10, 1000);
>>>>> +       if (ret)
>>>>> +               return ret;
>>>>> +
>>>>> +       /* Disable */
>>>>> +       regmap_update_bits(priv->regmap, MSR_CLK_REG0, MSR_ENABLE, 0);
>>>>> +
>>>>> +       /* Get the value in MHz*64 */
>>>>> +       regmap_read(priv->regmap, MSR_CLK_REG2, &val);
>>>>> +
>>>>> +       return (((val + 31) & MSR_VAL_MASK) / 64) * 1000000;
>>>>> +}
>>>>> +
>>>>> +static int clk_msr_show(struct seq_file *s, void *data)
>>>>> +{
>>>>> +       struct meson_gx_msr_id *clk_msr_id = s->private;
>>>>> +       int val;
>>>>> +
>>>>> +       val = meson_gx_measure_id(clk_msr_id->priv, clk_msr_id->id);
>>>>> +       if (val < 0)
>>>>> +               return val;
>>>>> +
>>>>> +       seq_printf(s, "%d\n", val);
>>>
>>> With jerome, we managed to have a much higher precision by cycling over the divider
>>> and checking when the counter overflows. And I will print the precision in the clock debugfs
>>> entry.
>> great that you could even improve the precision!
>>
>>>>> +
>>>>> +       return 0;
>>>>> +}
>>>>> +DEFINE_SHOW_ATTRIBUTE(clk_msr);
>>>> have you considered modelling this as clock driver instead?
>>>
>>> Yes, but it can wait.
>>> Actually this clk-msr can be feed to GEN_CLK and be outputted to a pad,
>>> but all this is only for debug, so we can stick to debugfs for now.
>>>
>>> Question, should I separate the clocks in a subdirectory and add a summary file like
>>> for the clk debugfs ?
>>>
>>>
>>> /sys/kernel/debug/meson-clk-msr
>>> ------------------|--- summary
>>> ------------------|--- clks
>>> -----------------------|--- ring_osc_out_ee_0
>>> ...
>>> -----------------------|--- ge2d
>>>
>>> ?
>> this is exactly why I was curious if you considered implementing this
>> as clock driver instead
>> based on your description above each measured clock will have the
>> following properties:
>> - id (passed to the clkmsr IP block)
>> - name (human readable name)
>> - clock rate
>> - accuracy
>>
>> doesn't CCF provide everything except "id"? you'll even get the summary
>>
>> can you explain how you would use the clkmsr output?
>> here's how I would use it:
>> - assume I'm debugging something broken
>> - I suspect that it may be due to the clock setup
>> - grep "suspicious-clock" /sys/kernel/debug/clk/clk_summary
>> - compare the grep output with /sys/kernel/debug/meson-clk-msr/suspicious-clock
>>
>> if it was a CCF driver I could simply do:
>> grep "suspicious-clock" /sys/kernel/debug/clk/clk_summary
>> -> this would return "suspicious-clock" (which is what the kernel can
>> configure) and "clkmsr_suspicious-clock" (which is what clkmsr reads)

I'm concerned because it will add a bunch of duplicate clock that will be measured each time you cat clk_summary...

I'm alsi concerned by the "CCF clock provider" feature, meaning we could feed the CLK_GEN with the clock selected
by the clk-msr, but this mean we won't be able to change the measured clock at will, only the CCF will select the
clock to measure. and we will loose the ability to have a summary of all internal clocks from debugfs.

> 
> Even futther, Couldn't this measure IP be used by the current CCF code
> (as an additonal, optional property) such the the debugfs clk_summary
> uses it directly?

It will need hacking the CCF core, but as Jerome and I said, this can be done later on !
We can push a debugfs version and migrate it to CCF when we figure out how to integrate it
correctly.

> 
> Kevin
> 
Neil

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