linux-kernel - Re: [PATCH v3 3/3] clk: qcom: Add display clock controller driver for SDM845

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Date:   Sun, 08 Jul 2018 23:16:50 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Taniya Das <tdas@...eaurora.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Amit Nischal <anischal@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] clk: qcom: Add display clock controller driver for SDM845

Quoting Taniya Das (2018-07-08 20:38:03)
> Hello Stephen,
> 
> Thanks for your review comments.
> 
> On 7/9/2018 5:24 AM, Stephen Boyd wrote:
> > Quoting Taniya Das (2018-06-23 07:19:27)
> >> diff --git a/drivers/clk/qcom/dispcc-sdm845.c b/drivers/clk/qcom/dispcc-sdm845.c
> >> new file mode 100644
> >> index 0000000..af437e0
> >> --- /dev/null
> >> +++ b/drivers/clk/qcom/dispcc-sdm845.c
> >> @@ -0,0 +1,674 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> > [...]
> >> +static struct clk_alpha_pll disp_cc_pll0 = {
> >> +       .offset = 0x0,
> >> +       .regs = clk_alpha_pll_regs[CLK_ALPHA_PLL_TYPE_FABIA],
> >> +       .clkr = {
> >> +               .hw.init = &(struct clk_init_data){
> >> +                       .name = "disp_cc_pll0",
> >> +                       .parent_names = (const char *[]){ "bi_tcxo" },
> >> +                       .num_parents = 1,
> >> +                       .ops = &clk_alpha_pll_fabia_ops,
> >> +               },
> >> +       },
> >> +};
> >> +
> >> +static struct clk_rcg2 disp_cc_mdss_byte0_clk_src = {
> >> +       .cmd_rcgr = 0x20d0,
> >> +       .mnd_width = 0,
> >> +       .hid_width = 5,
> >> +       .parent_map = disp_cc_parent_map_0,
> >> +       .clkr.hw.init = &(struct clk_init_data){
> >> +               .name = "disp_cc_mdss_byte0_clk_src",
> >> +               .parent_names = disp_cc_parent_names_0,
> >> +               .num_parents = 4,
> >> +               .flags = CLK_SET_RATE_PARENT | CLK_GET_RATE_NOCACHE,
> > 
> > Why is there the no cache flag? Last time I asked I don't think I got
> > any answer, and there isn't a comment here so please at least add a
> > comment to the code so we don't forget.
> >
> 
> I think you missed my comment from the earlier email. I would add the 
> comment and submit again.

Hmm.. ok.

> 
>  > Why is the nocache flag needed? Applies to all clks in this file.
>  >
> 
> This flag is required for all RCGs whose PLLs are controlled outside the 
> clock controller. The display code would require the recalculated rate 
> always.

Right. Why is the PLL controlled outside of the clock controller? The
rate should propagate upward to the PLL from here, so who's going
outside of that?