Re: [PATCH 06/19] clk: sunxi-ng: add support for the Allwinner V861 CCU

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] clk: sunxi-ng: ccu_mp_set_rate() ignores
  CCU_FEATURE_UPDATE_BIT for dram_clk
--

commit 4dcfa888826dc579312b5e254290daa03aed3f59
Author: Han Gao <gaohan@iscas.ac.cn>

clk: sunxi-ng: add support for the Allwinner V861 CCU

This commit adds the main CCU clock and reset driver for the Allwinner
V861 SoC.

> diff --git a/drivers/clk/sunxi-ng/ccu-sun252i-v861.c b/drivers/clk/sunxi-ng/ccu-sun252i-v861.c
> new file mode 100644
> index 0000000000000..af84c49fbaf16
> --- /dev/null
> +++ b/drivers/clk/sunxi-ng/ccu-sun252i-v861.c
[ ... ]
> +static const struct clk_parent_data dram_parents[] = {
> +	{ .fw_name = "hosc" },
> +	{ .hw = &pll_ddr_clk.common.hw },
> +	{ .hw = &pll_periph0_2x_clk.common.hw },
> +	{ .hw = &pll_periph0_800M_clk.common.hw },
> +};
> +
> +static SUNXI_CCU_MP_DATA_WITH_MUX_GATE_FEAT(dram_clk, "dram", dram_parents,
> +					    0x800,
> +					    0, 5,	/* M */
> +					    8, 2,	/* P */
> +					    24, 3,	/* mux */
> +					    BIT(31),	/* gate */
> +					    CLK_IS_CRITICAL,
> +					    CCU_FEATURE_UPDATE_BIT);

[Severity: Medium]
Does changing the rate of dram_clk actually latch the new dividers in
hardware?

dram_clk uses ccu_mp_ops with CCU_FEATURE_UPDATE_BIT, but unlike
ccu_div_set_rate(), ccu_mp_set_rate() never checks CCU_FEATURE_UPDATE_BIT
or sets CCU_SUNXI_UPDATE_BIT before writing the register:

drivers/clk/sunxi-ng/ccu_mp.c:ccu_mp_set_rate() {
    ...
	if (shift)
		reg |= ilog2(p) << cmp->p.shift;
	else
		reg |= (p - cmp->p.offset) << cmp->p.shift;

	writel(reg, cmp->common.base + cmp->common.reg);
    ...
}

When clk_set_rate() updates the M or P dividers without a parent mux or
gate change, the hardware ignores the unlatched divider update while
ccu_mp_recalc_rate() reads back the new register fields and reports the
wrong rate to the clock framework and child clocks such as mbus_clk.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261114-v861-v1-0-eb71ec3ee523@iscas.ac.cn?part=6