From: Frank Li <Frank.li@nxp.com>
To: "Peng Fan (OSS)" <peng.fan@oss.nxp.com>
Cc: abelvesa@kernel.org, mturquette@baylibre.com, sboyd@kernel.org,
shawnguo@kernel.org, s.hauer@pengutronix.de,
kernel@pengutronix.de, festevam@gmail.com, imx@lists.linux.dev,
linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Peng Fan <peng.fan@nxp.com>
Subject: Re: [PATCH] clk: imx: lpcg-scu: SW workaround for errata (e10858)
Date: Wed, 28 Feb 2024 14:17:22 -0500 [thread overview]
Message-ID: <Zd+GwrE5IvDgZX/c@lizhi-Precision-Tower-5810> (raw)
In-Reply-To: <20240228082649.1633083-1-peng.fan@oss.nxp.com>
On Wed, Feb 28, 2024 at 04:26:49PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@nxp.com>
>
> Back-to-back LPCG writes can be ignored by the LPCG register due to
> a HW bug. The writes need to be separated by at least 4 cycles of
> the gated clock.
>
> The workaround is implemented as follows:
> 1. For clocks running greater than or equal to 24MHz, a read
> followed by the write will provide sufficient delay.
> 2. For clocks running below 24MHz, add a delay of 4 clock cylces
> after the write to the LPCG register.
>
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
Fixes tag?
Frank
>
> This is to upstream a downstream patch that goes through many releases
> in several years. It maybe hard to trigger, but to address potential
> issues, let's add this workaround.
>
> drivers/clk/imx/clk-lpcg-scu.c | 33 ++++++++++++++++++++++++++++++---
> 1 file changed, 30 insertions(+), 3 deletions(-)
>
> 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)
> +{
> + writel(val, reg);
> +
> + if (rate >= 24000000 || rate == 0) {
> + u32 reg1;
> +
> + /*
> + * 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);
>
> spin_unlock_irqrestore(&imx_lpcg_scu_lock, flags);
>
> @@ -74,7 +101,7 @@ static void clk_lpcg_scu_disable(struct clk_hw *hw)
>
> reg = readl_relaxed(clk->reg);
> reg &= ~(CLK_GATE_SCU_LPCG_MASK << clk->bit_idx);
> - writel(reg, clk->reg);
> + do_lpcg_workaround(clk_hw_get_rate(hw), clk->reg, reg);
>
> spin_unlock_irqrestore(&imx_lpcg_scu_lock, flags);
> }
> @@ -151,7 +178,7 @@ static int __maybe_unused imx_clk_lpcg_scu_resume(struct device *dev)
> */
>
> writel(clk->state, clk->reg);
> - writel(clk->state, clk->reg);
> + do_lpcg_workaround(0, clk->reg, clk->state);
> dev_dbg(dev, "restore lpcg state 0x%x\n", clk->state);
>
> return 0;
> --
> 2.37.1
>
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next prev parent reply other threads:[~2024-02-28 19:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-28 8:26 [PATCH] clk: imx: lpcg-scu: SW workaround for errata (e10858) Peng Fan (OSS)
2024-02-28 19:17 ` Frank Li [this message]
2024-02-28 22:18 ` Stephen Boyd
-- strict thread matches above, loose matches on Subject: below --
2020-09-08 9:14 peng.fan
2020-09-08 10:18 ` Abel Vesa
2020-09-08 12:10 ` Peng Fan
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