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

Taniya Das
2019-09-27T07:38:06Z

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 :).

>>
>>>>
>>>> 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?

>>
>>>>
>>>>>
>>>>>> + .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.

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