linux-kernel - Re: [PATCH 2/2] clk: qcom: Add display clock controller driver for SDM845

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Date:   Tue, 19 Jun 2018 08:22:09 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Taniya Das <tdas@...eaurora.org>, robh@...nel.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,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] clk: qcom: Add display clock controller driver for SDM845

Quoting Taniya Das (2018-06-13 02:18:59)
> Hello Stephen,
> 
> Thanks for review.
> 
> On 6/12/2018 1:25 PM, Stephen Boyd wrote:
> > Quoting Taniya Das (2018-06-04 00:56:25)
> >> diff --git a/drivers/clk/qcom/dispcc-sdm845.c b/drivers/clk/qcom/dispcc-sdm845.c
> >> new file mode 100644
> >> index 0000000..317ab33
> >> --- /dev/null
> >> +++ b/drivers/clk/qcom/dispcc-sdm845.c
> 
> >> +#include "common.h"
> >> +#include "gdsc.h"
> >> +#include "reset.h"
> >> +
> >> +#define F(f, s, h, m, n) { (f), (s), (2 * (h) - 1), (m), (n) }
> > 
> > We really need to move this into the header file.
> > 
> > $ git grep '#define F(' -- drivers/clk/qcom/ | wc -l
> > 13
> > 
> Sure, will move this in a header and submit the patch.

Thanks!

> >> +
> >> +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_pclk0_clk_src = {
> >> +       .cmd_rcgr = 0x2058,
> >> +       .mnd_width = 8,
> >> +       .hid_width = 5,
> >> +       .parent_map = disp_cc_parent_map_4,
> >> +       .clkr.hw.init = &(struct clk_init_data){
> >> +               .name = "disp_cc_mdss_pclk0_clk_src",
> >> +               .parent_names = disp_cc_parent_names_4,
> >> +               .num_parents = 4,
> >> +               .flags = CLK_SET_RATE_PARENT | CLK_GET_RATE_NOCACHE,
> > 
> > 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.

That doesn't really answer the question. It seems to describe some sort
of problem with the PLL being controlled outside the clk controller/clk
framework. Please add more details and comments into the code here.

> 
> >> +               .ops = &clk_pixel_ops,
> >> +       },
> >> +};
> >> +
> >> +static struct clk_rcg2 disp_cc_mdss_pclk1_clk_src = {
> >> +       .cmd_rcgr = 0x2070,
> >> +       .mnd_width = 8,
> >> +       .hid_width = 5,
> >> +       .parent_map = disp_cc_parent_map_4,
> >> +       .clkr.hw.init = &(struct clk_init_data){
> > [...]
> >> +
> >> +static const struct regmap_config disp_cc_sdm845_regmap_config = {
> >> +       .reg_bits       = 32,
> >> +       .reg_stride     = 4,
> >> +       .val_bits       = 32,
> >> +       .max_register   = 0x10000,
> > 
> > This seems arbitrarily large. List the actual end?
> > 
> The actual end is larger than this :( , I have listed the range till the 
> register offset are used here.

Ok.

> 
> >> +       .fast_io        = true,
> >> +};
> >> +
> >> +static const struct qcom_cc_desc disp_cc_sdm845_desc = {
> >> +       .config = &disp_cc_sdm845_regmap_config,
> >> +       .clks = disp_cc_sdm845_clocks,
> >> +       .num_clks = ARRAY_SIZE(disp_cc_sdm845_clocks),
> >> +       .resets = disp_cc_sdm845_resets,
> >> +       .num_resets = ARRAY_SIZE(disp_cc_sdm845_resets),
> >> +       .gdscs = disp_cc_sdm845_gdscs,
> >> +       .num_gdscs = ARRAY_SIZE(disp_cc_sdm845_gdscs),
> >> +};
> >> +
> >> +static const struct of_device_id disp_cc_sdm845_match_table[] = {
> >> +       { .compatible = "qcom,sdm845-dispcc" },
> >> +       { }
> >> +};
> >> +MODULE_DEVICE_TABLE(of, disp_cc_sdm845_match_table);
> >> +
> >> +static int disp_cc_sdm845_probe(struct platform_device *pdev)
> >> +{
> >> +       struct regmap *regmap;
> >> +
> >> +       regmap = qcom_cc_map(pdev, &disp_cc_sdm845_desc);
> >> +       if (IS_ERR(regmap))
> >> +               return PTR_ERR(regmap);
> >> +
> >> +       clk_fabia_pll_configure(&disp_cc_pll0, regmap, &disp_cc_pll0_config);
> >> +
> >> +       /* Enable clock gating for DSI and MDP clocks */
> > 
> > Hardware clock gating? What does this mean.
> > 
> These are used for deciding whether to enable HW based Clock gating or 
> not. Setting these bit will enable HW based Clock gating.

Please state it's hardware clock gating then in the comment.

> 
> >> +       regmap_update_bits(regmap, 0x8000, 0x7f0, 0x7f0);
> >> +
> >> +       return qcom_cc_really_probe(pdev, &disp_cc_sdm845_desc, regmap);
> >> +}
>