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

[Stephen Boyd <sboyd@kernel.org>]

Quoting Taniya Das (2019-09-25 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?

> 
> >>
> >> 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?

> 
> >>
> >>>
> >>>> +       .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?