linux-kernel - Re: [PATCH v3 4/5] clk: stm32: Fix stm32f429 ltdc driver loading hang in clk set rate. keep ltdc clk running after kernel startup

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Message-ID: <158949014721.215346.12197373767247910756@swboyd.mtv.corp.google.com>
Date:   Thu, 14 May 2020 14:02:27 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     airlied@...ux.ie, alexandre.torgue@...com, daniel@...ll.ch,
        dillon.minfei@...il.com, mcoquelin.stm32@...il.com,
        mturquette@...libre.com, robh+dt@...nel.org, sam@...nborg.org,
        thierry.reding@...il.com
Cc:     devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-clk@...r.kernel.org,
        dillon.minfei@...il.com
Subject: Re: [PATCH v3 4/5] clk: stm32: Fix stm32f429 ltdc driver loading hang in clk set rate. keep ltdc clk running after kernel startup

Quoting dillon.minfei@...il.com (2020-05-12 00:03:36)
> From: dillon min <dillon.minfei@...il.com>
> 
> as store stm32f4_rcc_register_pll return to the wrong offset of clks,

Use () on functions, i.e. stm32f4_rcc_register_pll().

> so ltdc gate clk is null. need change clks[PLL_VCO_SAI] to clks[PLL_SAI]

And quote variables like 'clks[PLL_VCO_SAI]'

> 
> add CLK_IGNORE_UNUSED for ltdc to make sure clk not be freed by
> clk_disable_unused

clk_disable_unused() doesn't free anything. Why does ltdc not need to be
turned off if it isn't used? Is it critical to system operation? Should
it be marked with the critical clk flag then? The CLK_IGNORE_UNUSED flag
is almost always wrong to use.

> 
> Signed-off-by: dillon min <dillon.minfei@...il.com>
> ---
>  drivers/clk/clk-stm32f4.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/clk-stm32f4.c b/drivers/clk/clk-stm32f4.c
> index 18117ce..0ba73de 100644
> --- a/drivers/clk/clk-stm32f4.c
> +++ b/drivers/clk/clk-stm32f4.c
> @@ -129,7 +129,8 @@ static const struct stm32f4_gate_data stm32f429_gates[] __initconst = {
>         { STM32F4_RCC_APB2ENR, 20,      "spi5",         "apb2_div" },
>         { STM32F4_RCC_APB2ENR, 21,      "spi6",         "apb2_div" },
>         { STM32F4_RCC_APB2ENR, 22,      "sai1",         "apb2_div" },
> -       { STM32F4_RCC_APB2ENR, 26,      "ltdc",         "apb2_div" },
> +       { STM32F4_RCC_APB2ENR, 26,      "ltdc",         "apb2_div",
> +               CLK_IGNORE_UNUSED },
>  };
>  
>  static const struct stm32f4_gate_data stm32f469_gates[] __initconst = {
> @@ -1757,7 +1758,7 @@ static void __init stm32f4_rcc_init(struct device_node *np)
>         clks[PLL_VCO_I2S] = stm32f4_rcc_register_pll("vco_in",
>                         &data->pll_data[1], &stm32f4_clk_lock);
>  
> -       clks[PLL_VCO_SAI] = stm32f4_rcc_register_pll("vco_in",
> +       clks[PLL_SAI] = stm32f4_rcc_register_pll("vco_in",
>                         &data->pll_data[2], &stm32f4_clk_lock);
>  
>         for (n = 0; n < MAX_POST_DIV; n++) {