Re: [PATCH v3 3/3] clk: qcom: Add Global Clock controller (GCC) driver for SC7180

Taniya Das
2019-10-03T10:31:25Z

Hi Stephen,

On 10/1/2019 8:08 PM, Stephen Boyd wrote:
> Quoting Taniya Das (2019-09-27 00:37:57)
>> Hi Stephen,
>>
>> On 9/25/2019 6:33 PM, Stephen Boyd wrote:
>>> Quoting Taniya Das (2019-09-25 04:20:07)
>>>> Hi Stephen,
>>>>
>>>> Please find my comments.
>>>>
>>>> On 9/25/2019 4:42 AM, Stephen Boyd wrote:
>>>>> Quoting Taniya Das (2019-09-23 01:01:11)
>>>>>> Hi Stephen,
>>>>>>
>>>>>> Thanks for your comments.
>>>>>>
>>>>>> On 9/19/2019 3:09 AM, Stephen Boyd wrote:
>>>>>>> Quoting Taniya Das (2019-09-18 02:50:18)
>>>>>>>> diff --git a/drivers/clk/qcom/gcc-sc7180.c b/drivers/clk/qcom/gcc-sc7180.c
>>>>>>>> new file mode 100644
>>>>>>>> index 000000000000..d47865d5408f
>>>>>>>> --- /dev/null
>>>>>>>> +++ b/drivers/clk/qcom/gcc-sc7180.c
>>>>>>>> + .ops = &clk_branch2_ops,
>>>>>>>> + },
>>>>>>>> + },
>>>>>>>> +};
>>>>>>>> +
>>>>> [...]
>>>>>>>> +static struct clk_branch gcc_ufs_phy_phy_aux_clk = {
>>>>>>>> + .halt_reg = 0x77094,
>>>>>>>> + .halt_check = BRANCH_HALT,
>>>>>>>> + .hwcg_reg = 0x77094,
>>>>>>>> + .hwcg_bit = 1,
>>>>>>>> + .clkr = {
>>>>>>>> + .enable_reg = 0x77094,
>>>>>>>> + .enable_mask = BIT(0),
>>>>>>>> + .hw.init = &(struct clk_init_data){
>>>>>>>> + .name = "gcc_ufs_phy_phy_aux_clk",
>>>>>>>> + .parent_data = &(const struct clk_parent_data){
>>>>>>>> + .hw = &gcc_ufs_phy_phy_aux_clk_src.clkr.hw,
>>>>>>>> + },
>>>>>>>> + .num_parents = 1,
>>>>>>>> + .flags = CLK_SET_RATE_PARENT,
>>>>>>>> + .ops = &clk_branch2_ops,
>>>>>>>> + },
>>>>>>>> + },
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +static struct clk_branch gcc_ufs_phy_rx_symbol_0_clk = {
>>>>>>>> + .halt_reg = 0x7701c,
>>>>>>>> + .halt_check = BRANCH_HALT_SKIP,
>>>>>>>
>>>>>>> Again, nobody has fixed the UFS driver to not need to do this halt skip
>>>>>>> check for these clks? It's been over a year.
>>>>>>>
>>>>>>
>>>>>> The UFS_PHY_RX/TX clocks could be left enabled due to certain HW boot
>>>>>> configuration and thus during the late initcall of clk_disable there
>>>>>> could be warnings of "clock stuck ON" in the dmesg. That is the reason
>>>>>> also to use the BRANCH_HALT_SKIP flag.
>>>>>
>>>>> Oh that's bad. Why do the clks stay on when we try to turn them off?
>>>>>
>>>>
>>>> Those could be due to the configuration selected by HW and SW cannot
>>>> override them, so traditionally we have never polled for CLK_OFF for
>>>> these clocks.
>>>
>>> Is that the case or just a guess?
>>>
>>
>> This is the behavior :).
>
> Ok. It's the same as sdm845 so I guess it's OK.
>

Thanks.

>>
>>>>
>>>>>>
>>>>>> I would also check internally for the UFS driver fix you are referring here.
>>>>>
>>>>> Sure. I keep asking but nothing is done :(
>>>>>
>>>>>>
>>>>>>>> + .clkr = {
>>>>>>>> + .enable_reg = 0x7701c,
>>>>>>>> + .enable_mask = BIT(0),
>>>>>>>> + .hw.init = &(struct clk_init_data){
>>>>>>>> + .name = "gcc_ufs_phy_rx_symbol_0_clk",
>>>>>>>> + .ops = &clk_branch2_ops,
>>>>>>>> + },
>>>>>>>> + },
>>>>>>>> +};
>>>>>>>> +
>>>>> [...]
>>>>>>>> +
>>>>>>>> +static struct clk_branch gcc_usb3_prim_phy_pipe_clk = {
>>>>>>>> + .halt_reg = 0xf058,
>>>>>>>> + .halt_check = BRANCH_HALT_SKIP,
>>>>>>>
>>>>>>> Why does this need halt_skip?
>>>>>>
>>>>>> This is required as the source is external PHY, so we want to not check
>>>>>> for HALT.
>>>>>
>>>>> This doesn't really answer my question. If the source is an external phy
>>>>> then it should be listed as a clock in the DT binding and the parent
>>>>> should be specified here. Unless something doesn't work because of that?
>>>>>
>>>>
>>>> The USB phy is managed by the USB driver and clock driver is not aware
>>>> if USB driver models the phy as a clock. Thus we do want to keep a
>>>> dependency on the parent and not poll for CLK_ENABLE.
>>>
>>> The clk driver should be aware of the USB driver modeling the phy as a
>>> clk. We do that for other phys so what is the difference here?
>>>
>>
>> Let me check with the USB team, but could we keep them for now?
>
> Ok. It's also the same as sdm845 so I guess it's OK. Would be nice to
> properly model it though so we can be certain the clk is actually
> enabled.
>

I am going to follow it up and close on this.

>>
>>>>
>>>>>>
>>>>>>>
>>>>>>>> + .clkr = {
>>>>>>>> + .enable_reg = 0xf058,
>>>>>>>> + .enable_mask = BIT(0),
>>>>>>>> + .hw.init = &(struct clk_init_data){
>>>>>>>> + .name = "gcc_usb3_prim_phy_pipe_clk",
>>>>>>>> + .ops = &clk_branch2_ops,
>>>>>>>> + },
>>>>>>>> + },
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +static struct clk_branch gcc_usb_phy_cfg_ahb2phy_clk = {
>>>>>>>> + .halt_reg = 0x6a004,
>>>>>>>> + .halt_check = BRANCH_HALT,
>>>>>>>> + .hwcg_reg = 0x6a004,
>>>>>>>> + .hwcg_bit = 1,
>>>>>>>> + .clkr = {
>>>>>>>> + .enable_reg = 0x6a004,
>>>>>>>> + .enable_mask = BIT(0),
>>>>>>>> + .hw.init = &(struct clk_init_data){
>>>>>>>> + .name = "gcc_usb_phy_cfg_ahb2phy_clk",
>>>>>>>> + .ops = &clk_branch2_ops,
>>>>>>>> + },
>>>>>>>> + },
>>>>>>>> +};
>>>>>>>> +
>>>>>>>> +/* Leave the clock ON for parent config_noc_clk to be kept enabled */
>>>>>>>
>>>>>>> There's no parent though... So I guess this means it keeps it enabled
>>>>>>> implicitly in hardware?
>>>>>>>
>>>>>>
>>>>>> These are not left enabled, but want to leave them enabled for clients
>>>>>> on config NOC.
>>>>>
>>>>> Sure. It just doesn't make sense to create clk structures and expose
>>>>> them in the kernel when we just want to turn the bits on and leave them
>>>>> on forever. Why not just do some register writes in probe for this
>>>>> driver? Doesn't that work just as well and use less memory?
>>>>>
>>>>
>>>> Even if I write these registers during probe, the late init check
>>>> 'clk_core_is_enabled' would return true and would be turned OFF, that is
>>>> the reason for marking them CRITICAL.
>>>>
>>>
>>> That wouldn't happen if the clks weren't registered though, no?
>>>
>>
>> I want to keep these clock CRITICAL and registered for now, but we
>> should be able to revisit/clean them up later.
>>
>
> Why do you want to keep them critical and registered? I'm suggesting
> that any clk that is marked critical and doesn't have a parent should
> instead become a register write in probe to turn the clk on.
>
Sure, let me do a one-time enable from probe for the clocks which
doesn't have a parent.
But I would now have to educate the clients of these clocks to remove
using them.

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