[PATCH 1/7] clk: stm32mp1: Split ETHCK_K into separate MUX and GATE clock
gabriel.fernandez at foss.st.com
gabriel.fernandez at foss.st.com
Mon Apr 19 08:46:27 BST 2021
Hi Marek,
On 4/16/21 5:31 PM, Marek Vasut wrote:
> On 4/16/21 5:23 PM, Alexandre TORGUE wrote:
>
> Hello Alexandre,
>
>> On 4/16/21 3:47 PM, Marek Vasut wrote:
>>> On 4/16/21 8:44 AM, gabriel.fernandez at foss.st.com wrote:
>>>> Hi Marek
>>>
>>> Hello Gabriel,
>>>
>>>> On 4/14/21 4:04 PM, Marek Vasut wrote:
>>>>> On 4/14/21 3:03 PM, gabriel.fernandez at foss.st.com wrote:
>>>>>> Hi Marek,
>>>>>
>>>>> Hello Gabriel,
>>>>>
>>>>>> Thanks for the patchset
>>>>>>
>>>>>> On 4/8/21 8:57 PM, Marek Vasut wrote:
>>>>>>> The ETHCK_K are modeled as composite clock of MUX and GATE,
>>>>>>> however per
>>>>>>> STM32MP1 Reference Manual RM0436 Rev 3, Page 574, Figure 83.
>>>>>>> Peripheral
>>>>>>> clock distribution for Ethernet, ETHPTPDIV divider is attached
>>>>>>> past the
>>>>>>> ETHCK_K mux, and ETH_CLK/eth_clk_fb clock are output past ETHCKEN
>>>>>>> gate.
>>>>>>> Therefore, in case ETH_CLK/eth_clk_fb are not in use AND PTP
>>>>>>> clock are
>>>>>>> in use, ETHCKEN gate can be turned off. Current driver does not
>>>>>>> permit
>>>>>>> that, fix it.
>>>>>>
>>>>>> I don"t understand, it's already the case.
>>>>>>
>>>>>> ETHCK_K it's a composite with a MUX and a GATE.
>>>>>
>>>>> But ETHCK_K is _not_ a composite clock, look at the Figure 83 in
>>>>> the datasheet again and schematic below.
>>>>>
>>>>>> ETHPTP_K (ETHPTPDIV) it's a composite with the same MUX and a DIV
>>>>>> (no gate)
>>>>>
>>>>> But ETHPTP_K shouldn't control any mux, it is only a divider.
>>>>>
>>>>>> If you use only ETHPTPDIV, ETHCKEN gate can be turned off.
>>>>>
>>>>> Look, this is what you have today:
>>>>>
>>>>> .------------ ETHCK_K -----------.
>>>>> |_______ _______ |
>>>>> pll4_p_ck--|M_ETHCK\ |G_ETHCK\ |
>>>>> | MUX |------+-----| GATE |-------------[x] ETH_CLK
>>>>> pll3_q_ck--|_______/ | |_______/ eth_clk_fb
>>>>> | |
>>>>> | '--(ETHCKSELR[7:4] divider)--[x]
>>>>> clk_ptp_ref
>>>>> | |
>>>>> '------------ ETHPTP_K --------------------'
>>>>>
>>>>> And this is what you should have, to avoid having two composite
>>>>> clock which control the same mux using the same register bit, i.e.
>>>>> what this patch implements:
>>>>>
>>>>> .- ck_ker_eth -. .--- ETHCK_K --.
>>>>> |_______ | | _______ |
>>>>> pll4_p_ck--|M_ETHCK\ | | |G_ETHCK\ |
>>>>> | MUX |------+-----| GATE |-------------[x] ETH_CLK
>>>>> pll3_q_ck--|_______/ | |_______/ eth_clk_fb
>>>>> |
>>>>> '--(ETHCKSELR[7:4] divider)--[x]
>>>>> clk_ptp_ref
>>>>> | |
>>>>> '---- ETHPTP_K -----------'
>>>>>
>>>>
>>>> These 2 solutions are valid. I made the choice to implement the
>>>> first one to be able to change parent with the kernel clock of the
>>>> IP (no need to add an intermediate binding).
>>>
>>> Which IP are you talking about in here ?
>>>
>>>> It's the same principle for all kernel of this soc.
>>>
>>> The first option is wrong, because in that model, you have two
>>> composite clock which control the same one mux bit in the same
>>> register. Basically you register two distinct clock which operate the
>>> same hardware knob.
>>>
>>>> I can ask to Alexandre to comeback of this principle, but i 'm not
>>>> favorable.
>>>
>>
>> The only discussing thing is how the clock is shown. I mean either two
>> composites or one mux plus two gates. Gabriel made a choice to
>> abstract the mux in two composite clocks. But it seems that at the end
>> we have the same behaviour, isn't ?
>
> Not really. Since the two composite clock control the same mux bit,
> consider what would happen if you were to select pll4_p_ck as parent for
> one (e.g. ETHCK_K), and pll3_q_ck as parent for the other (e.g.
> ETHPTP_K), what would be the result ? I guess the result would depend on
> when the reparenting of each ETHCK_K/ETHPTP_K happens on boot, and I
> don't think that's how it should work. With a single mux controlling
> that one single bit, such situation wouldn't happen.
The reparenting is managed. This mux has specific ops.
root at stm32mp1-disco-oss:~# cat /sys/kernel/debug/clk/ethck_k/clk_parent
&& cat /sys/kernel/debug/clk/ethptp_k/clk_parent
pll4_p
pll4_p
root at stm32mp1-disco-oss:~# echo pll3_q >
/sys/kernel/debug/clk/ethptp_k/clk_set_parent
root at stm32mp1-disco-oss:~# cat /sys/kernel/debug/clk/ethck_k/clk_parent
&& cat /sys/kernel/debug/clk/ethptp_k/clk_parent
pll3_q
pll3_q
>
>> Adding "ck_ker_eth" would impose a new clock to take in DT ?
> Nope, the ck_ker_eth is without ID and internal to the driver. They
> exist only to describe the clock tree correctly.
>
> [...]
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