linux-kernel - Re: [PATCH v2] clk: sunxi-ng: sun50i: h6: Modify GPU clock configuration to support DFS

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Message-ID: <CAGphcdkZzjw-6oSnpiDM5YgPkuSV3VPX4nKo_FfPeg36MzT8Ew@mail.gmail.com>
Date:   Mon, 4 Jul 2022 12:54:06 +0300
From:   Roman Stratiienko <r.stratiienko@...il.com>
To:     Jernej Škrabec <jernej.skrabec@...il.com>
Cc:     Samuel Holland <samuel@...lland.org>,
        Clément Péron <peron.clem@...il.com>,
        Michael Turquette <mturquette@...libre.com>, sboyd@...nel.org,
        mripard@...nel.org, wens@...e.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] clk: sunxi-ng: sun50i: h6: Modify GPU clock
 configuration to support DFS

Hi Jernej,

вс, 3 июл. 2022 г. в 21:43, Jernej Škrabec <jernej.skrabec@...il.com>:
>
> Dne nedelja, 03. julij 2022 ob 18:45:14 CEST je Roman Stratiienko napisal(a):
> > Using simple bash script it was discovered that not all CCU registers
> > can be safely used for DFS, e.g.:
> >
> >     while true
> >     do
> >         devmem 0x3001030 4 0xb0003e02
> >         devmem 0x3001030 4 0xb0001e02
> >     done
> >
> > Script above changes the GPU_PLL multiplier register value. While the
> > script is running, the user should interact with the user interface.
> >
> > Using this method the following results were obtained:
> > | Register  | Name           | Bits  | Values | Result |
> > | --        | --             | --    | --     | --     |
> > | 0x3001030 | GPU_PLL.MULT   | 15..8 | 20-62  | OK     |
> > | 0x3001030 | GPU_PLL.INDIV  |     1 | 0-1    | OK     |
> > | 0x3001030 | GPU_PLL.OUTDIV |     0 | 0-1    | FAIL   |
> > | 0x3001670 | GPU_CLK.DIV    |  3..0 | ANY    | FAIL   |
> >
> > DVFS started to work seamlessly once dividers which caused the
> > glitches were set to fixed values.
> >
> > Signed-off-by: Roman Stratiienko <r.stratiienko@...il.com>
> >
> > ---
> >
> > Changelog:
> >
> > V2:
> > - Drop changes related to mux
> > - Drop frequency limiting
> > - Add unused dividers initialization
> > ---
> >  drivers/clk/sunxi-ng/ccu-sun50i-h6.c | 16 +++++++++++++---
> >  1 file changed, 13 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > b/drivers/clk/sunxi-ng/ccu-sun50i-h6.c index 2ddf0a0da526f..1b0205ff24108
> > 100644
> > --- a/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > +++ b/drivers/clk/sunxi-ng/ccu-sun50i-h6.c
> > @@ -95,13 +95,13 @@ static struct ccu_nkmp pll_periph1_clk = {
> >       },
> >  };
> >
> > +/* For GPU PLL, using an output divider for DFS causes system to fail */
> >  #define SUN50I_H6_PLL_GPU_REG                0x030
> >  static struct ccu_nkmp pll_gpu_clk = {
> >       .enable         = BIT(31),
> >       .lock           = BIT(28),
> >       .n              = _SUNXI_CCU_MULT_MIN(8, 8, 12),
> >       .m              = _SUNXI_CCU_DIV(1, 1), /* input divider */
> > -     .p              = _SUNXI_CCU_DIV(0, 1), /* output divider
> */
>
> Having minimum (288 MHz) as per vendor GPU driver and maximum, either max. opp
> or max. from datasheet is equally good. I know that both are basically limited
> with opp table, but people like to play with these, so it's good to have them
> in.
>
> >       .common         = {
> >               .reg            = 0x030,
> >               .hw.init        = CLK_HW_INIT("pll-gpu", "osc24M",
> > @@ -294,9 +294,9 @@ static SUNXI_CCU_M_WITH_MUX_GATE(deinterlace_clk,
> > "deinterlace", static SUNXI_CCU_GATE(bus_deinterlace_clk,
> > "bus-deinterlace", "psi-ahb1-ahb2", 0x62c, BIT(0), 0);
> >
> > +/* Keep GPU_CLK divider const to avoid DFS instability. */
> >  static const char * const gpu_parents[] = { "pll-gpu" };
> > -static SUNXI_CCU_M_WITH_MUX_GATE(gpu_clk, "gpu", gpu_parents, 0x670,
> > -                                    0, 3,    /* M */
> > +static SUNXI_CCU_MUX_WITH_GATE(gpu_clk, "gpu", gpu_parents, 0x670,
> >                                      24, 1,   /* mux */
> >                                      BIT(31), /* gate */
> >                                      CLK_SET_RATE_PARENT);
> > @@ -1193,6 +1193,16 @@ static int sun50i_h6_ccu_probe(struct platform_device
> > *pdev) if (IS_ERR(reg))
> >               return PTR_ERR(reg);
> >
> > +     /* Force PLL_GPU output divider to 0 */
>
> Divider  0 here
>
> > +     val = readl(reg + SUN50I_H6_PLL_GPU_REG);
> > +     val &= ~BIT(0);
> > +     writel(val, reg + SUN50I_H6_PLL_GPU_REG);
> > +
> > +     /* Force GPU_CLK divider to 0 */
>
> and here sounds wrong, since division by zero is not defined. Using 1 is more
> intuitive and correct, since that's what HW actually uses.
>

You're right but a few lines below there is already a similar message
(see below) , so I used similar formulation to avoid confusion.

        /*
         * Force the output divider of video PLLs to 0.
         *
         * See the comment before pll-video0 definition for the reason.
         */

> Patch looks good otherwise.

May I have your r-b?

Best regards,
Roman

>
> Best regards,
> Jernej
>
> > +     val = readl(reg + gpu_clk.common.reg);
> > +     val &= ~GENMASK(3, 0);
> > +     writel(val, reg + gpu_clk.common.reg);
> > +
> >       /* Enable the lock bits on all PLLs */
> >       for (i = 0; i < ARRAY_SIZE(pll_regs); i++) {
> >               val = readl(reg + pll_regs[i]);
>
>
>
>