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

[Stephen Boyd <sboyd@kernel.org>]

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.

> 
> >>
> >>>>
> >>>> 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.

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