linux-kernel - Re: [PATCH] clk: imx: lpcg-scu: SW workaround for errata (e10858)

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Date: Wed, 28 Feb 2024 14:18:03 -0800
From: Stephen Boyd <sboyd@...nel.org>
To: Peng Fan (OSS) <peng.fan@....nxp.com>, abelvesa@...nel.org, festevam@...il.com, kernel@...gutronix.de, mturquette@...libre.com, s.hauer@...gutronix.de, shawnguo@...nel.org
Cc: imx@...ts.linux.dev, linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Peng Fan <peng.fan@....com>
Subject: Re: [PATCH] clk: imx: lpcg-scu: SW workaround for errata (e10858)

Quoting Peng Fan (OSS) (2024-02-28 00:26:49)
> diff --git a/drivers/clk/imx/clk-lpcg-scu.c b/drivers/clk/imx/clk-lpcg-scu.c
> index dd5abd09f3e2..b30d0f8b5bca 100644
> --- a/drivers/clk/imx/clk-lpcg-scu.c
> +++ b/drivers/clk/imx/clk-lpcg-scu.c
> @@ -6,6 +6,7 @@
>  
>  #include <linux/bits.h>
>  #include <linux/clk-provider.h>
> +#include <linux/delay.h>
>  #include <linux/err.h>
>  #include <linux/io.h>
>  #include <linux/slab.h>
> @@ -41,6 +42,31 @@ struct clk_lpcg_scu {
>  
>  #define to_clk_lpcg_scu(_hw) container_of(_hw, struct clk_lpcg_scu, hw)
>  
> +/* e10858 -LPCG clock gating register synchronization errata */
> +static void do_lpcg_workaround(u32 rate, void __iomem *reg, u32 val)

unsigned long rate

> +{
> +       writel(val, reg);
> +
> +       if (rate >= 24000000 || rate == 0) {
> +               u32 reg1;

Please declare this variable at the start of the function.

> +
> +               /*
> +                * The time taken to access the LPCG registers from the AP core
> +                * through the interconnect is longer than the minimum delay
> +                * of 4 clock cycles required by the errata.
> +                * Adding a readl will provide sufficient delay to prevent
> +                * back-to-back writes.
> +                */
> +               reg1 = readl(reg);
> +       } else {
> +               /*
> +                * For clocks running below 24MHz, wait a minimum of
> +                * 4 clock cycles.
> +                */
> +               ndelay(4 * (DIV_ROUND_UP(1000000000, rate)));
> +       }
> +}
> +
>  static int clk_lpcg_scu_enable(struct clk_hw *hw)
>  {
>         struct clk_lpcg_scu *clk = to_clk_lpcg_scu(hw);
> @@ -57,7 +83,8 @@ static int clk_lpcg_scu_enable(struct clk_hw *hw)
>                 val |= CLK_GATE_SCU_LPCG_HW_SEL;
>  
>         reg |= val << clk->bit_idx;
> -       writel(reg, clk->reg);
> +
> +       do_lpcg_workaround(clk_hw_get_rate(hw), clk->reg, reg);

I'd prefer the name had 'writel' in it somewhere.
>  
>         spin_unlock_irqrestore(&imx_lpcg_scu_lock, flags);
>