Re: [PATCH v3 03/15] soc: tegra: Add Tegra PMC clock registrations into PMC driver

From: Dmitry Osipenko
Date: Tue Dec 10 2019 - 12:42:04 EST

10.12.2019 19:53, Sowjanya Komatineni ÐÐÑÐÑ:
> On 12/9/19 3:03 PM, Sowjanya Komatineni wrote:
>> On 12/9/19 12:46 PM, Sowjanya Komatineni wrote:
>>> On 12/9/19 12:12 PM, Dmitry Osipenko wrote:
>>>> 08.12.2019 00:36, Sowjanya Komatineni ÐÐÑÐÑ:
>>>>> On 12/7/19 11:59 AM, Sowjanya Komatineni wrote:
>>>>>> On 12/7/19 8:00 AM, Dmitry Osipenko wrote:
>>>>>>> 07.12.2019 18:53, Dmitry Osipenko ÐÐÑÐÑ:
>>>>>>>> 07.12.2019 18:47, Dmitry Osipenko ÐÐÑÐÑ:
>>>>>>>>> 07.12.2019 17:28, Dmitry Osipenko ÐÐÑÐÑ:
>>>>>>>>>> 06.12.2019 05:48, Sowjanya Komatineni ÐÐÑÐÑ:
>>>>>>>>>>> Tegra210 and prior Tegra PMC has clk_out_1, clk_out_2, clk_out_3
>>>>>>>>>>> with
>>>>>>>>>>> mux and gate for each of these clocks.
>>>>>>>>>>> Currently these PMC clocks are registered by Tegra clock driver
>>>>>>>>>>> using
>>>>>>>>>>> clk_register_mux and clk_register_gate by passing PMC base
>>>>>>>>>>> address
>>>>>>>>>>> and register offsets and PMC programming for these clocks
>>>>>>>>>>> happens
>>>>>>>>>>> through direct PMC access by the clock driver.
>>>>>>>>>>> With this, when PMC is in secure mode any direct PMC access
>>>>>>>>>>> from the
>>>>>>>>>>> non-secure world does not go through and these clocks will
>>>>>>>>>>> not be
>>>>>>>>>>> functional.
>>>>>>>>>>> This patch adds these clocks registration with PMC as a clock
>>>>>>>>>>> provider
>>>>>>>>>>> for these clocks. clk_ops callback implementations for these
>>>>>>>>>>> clocks
>>>>>>>>>>> uses tegra_pmc_readl and tegra_pmc_writel which supports PMC
>>>>>>>>>>> programming
>>>>>>>>>>> in secure mode and non-secure mode.
>>>>>>>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
>>>>>>>>>>> ---
>>>>>>>>> [snip]
>>>>>>>>>>> +
>>>>>>>>>>> +static const struct clk_ops pmc_clk_gate_ops = {
>>>>>>>>>>> +ÂÂÂ .is_enabled = pmc_clk_is_enabled,
>>>>>>>>>>> +ÂÂÂ .enable = pmc_clk_enable,
>>>>>>>>>>> +ÂÂÂ .disable = pmc_clk_disable,
>>>>>>>>>>> +};
>>>>>>>>>> What's the benefit of separating GATE from the MUX?
>>>>>>>>>> I think it could be a single clock.
>>>>>>>>> According to TRM:
>>>>>>>>> 1. GATE and MUX are separate entities.
>>>>>>>>> 2. GATE is the parent of MUX (see PMC's CLK_OUT paths diagram
>>>>>>>>> in TRM).
>>>>>>>>> 3. PMC doesn't gate EXTPERIPH clock but could "force-enable" it,
>>>>>>>>> correct?
>>>>> Was following existing clk-tegra-pmc as I am not sure of reason for
>>>>> having these clocks registered as separate mux and gate clocks.
>>>>> Yes, PMC clocks can be registered as single clock and can use clk_ops
>>>>> for set/get parent and enable/disable.
>>>>> enable/disable of PMC clocks is for force-enable to force the clock to
>>>>> run regardless of ACCEPT_REQ or INVERT_REQ.
>>>>>>>> 4. clk_m_div2/4 are internal PMC OSC dividers and thus these clocks
>>>>>>>> should belong to PMC.
>>>>>>> Also, it should be "osc" and not "clk_m".
>>>>>> I followed the same parents as it were in existing clk-tegra-pmc
>>>>>> driver.
>>>>>> Yeah they are wrong and they should be from osc and not clk_m.
>>>>>> Will fix in next version.
>> Reg clk_m_div2/3, they are dividers at OSC pad and not really internal
>> to PMC block.
>> current clock driver creates clk_m_div clocks which should actually be
>> osc_div2/osc_div4 clocks with osc as parent.
>> There are no clk_m_div2 and clk_m_div4 from clk_m
>> Will fix this in next version.
>>>> Could you please describe the full EXTPERIPH clock topology and how the
>>>> pinmux configuration is related to it all?
>>>> What is internal to the Tegra chip and what are the external outputs?
>>>> Is it possible to bypass PMC on T30+ for the EXTPERIPH clocks?
>>> PMC CLK1/2/3 possible sources are OSC_DIV1, OSC_DIV2, OSC_DIV4,
>>> OSC_DIV1/2/4 are with internal dividers at the OSC Pads
>>> EXTPERIPH is from CAR and it has reset and enable controls along with
>>> clock source selections to choose one of the PLLA_OUT0, CLK_S,
>>> So, PMC CLK1/2/4 possible parents are OSC_DIV1, OSC_DIV2, OSC_DIV4,
>>> CLK1/2/3 also has Pinmux to route EXTPERIPH output on to these pins.
>>> When EXTERN output clock is selected for these PMC clocks thru
>>> CLKx_SRC_SEL, output clock is from driver by EXTPERIPH from CAR via
>>> Pinmux logic or driven as per CLKx_SRC_SEL bypassing pinmux based on
>>> CLKx_ACCEPT_REQ bit.
>>> PMC Clock control register has bit CLKx_ACCEPT_REQ
>>> When CLKx_ACCEPT_REQ = 0, output clock driver is from by EXTPERIPH
>>> through the pinmux
>>> When CLKx_ACCEPT_REQ = 1, output clock is based on CLKx_SRC_SEL bits
>>> (OSC_DIV1/2/4 and EXTPERIPH clock bypassing the pinmux)
>>> FORCE_EN bit in PMC CLock control register forces the clock to run
>>> regardless of this.
> PMC clock gate is based on the state of CLKx_ACCEPT_REQ and FORCE_EN
> like explained above.
> CLKx_ACCEPT_REQ is 0 default and FORCE_EN acts as gate to enable/disable
> EXTPERIPH clock output to PMC CLK_OUT_1/2/3.

[and to enable OSC as well]

> So I believe we need to register as MUX and Gate rather than as a single
> clock. Please confirm.

1. The force-enabling is applied to both OSC and EXTERN sources of
PMC_CLK_OUT_x by PMC at once.

2. Both of PMC's force-enabling and OSC/EXTERN selection is internal to PMC.

Should be better to define it as a single "pmc_clk_out_x". I don't see
any good reasons for differentiating PMC's Gate from the MUX, it's a
single hardware unit from a point of view of the rest of the system.

Peter, do you have any objections?