linux-kernel - Re: [PATCH v4 2/2] clk: ingenic-tcu: Fix missing TCU clock for X1000 SoCs

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Message-Id: <FKM6AR.T3U5W4W42W2R3@crapouillou.net>
Date:   Mon, 11 Apr 2022 16:48:15 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
Cc:     robh+dt@...nel.org, krzk+dt@...nel.org, tsbogend@...ha.franken.de,
        mturquette@...libre.com, sboyd@...nel.org,
        linux-mips@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH v4 2/2] clk: ingenic-tcu: Fix missing TCU clock for X1000
 SoCs

Hi Aidan,

Le lun., avril 11 2022 at 16:42:41 +0100, Aidan MacDonald 
<aidanmacdonald.0x0@...il.com> a écrit :
> The TCU clock gate on X1000 wasn't requested by the driver and could
> be gated automatically later on in boot, which prevents timers from
> running and breaks PWM.
> 
> Add a workaround to support old device trees that don't specify the
> "tcu" clock gate. In this case the kernel will print a warning and
> attempt to continue without the clock, which is wrong, but it could
> work if "clk_ignore_unused" is in the kernel arguments.
> 
> Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@...il.com>
> ---
>  drivers/clk/ingenic/tcu.c | 38 ++++++++++++++++++++++++++------------
>  1 file changed, 26 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/clk/ingenic/tcu.c b/drivers/clk/ingenic/tcu.c
> index 77acfbeb4830..ce8c768db997 100644
> --- a/drivers/clk/ingenic/tcu.c
> +++ b/drivers/clk/ingenic/tcu.c
> @@ -31,6 +31,7 @@ struct ingenic_soc_info {
>  	unsigned int num_channels;
>  	bool has_ost;
>  	bool has_tcu_clk;
> +	bool allow_missing_tcu_clk;
>  };
> 
>  struct ingenic_tcu_clk_info {
> @@ -320,7 +321,8 @@ static const struct ingenic_soc_info 
> jz4770_soc_info = {
>  static const struct ingenic_soc_info x1000_soc_info = {
>  	.num_channels = 8,
>  	.has_ost = false, /* X1000 has OST, but it not belong TCU */
> -	.has_tcu_clk = false,
> +	.has_tcu_clk = true,
> +	.allow_missing_tcu_clk = true,
>  };
> 
>  static const struct of_device_id __maybe_unused 
> ingenic_tcu_of_match[] __initconst = {
> @@ -354,15 +356,27 @@ static int __init ingenic_tcu_probe(struct 
> device_node *np)
>  	if (tcu->soc_info->has_tcu_clk) {
>  		tcu->clk = of_clk_get_by_name(np, "tcu");
>  		if (IS_ERR(tcu->clk)) {
> -			ret = PTR_ERR(tcu->clk);
> -			pr_crit("Cannot get TCU clock\n");
> -			goto err_free_tcu;
> -		}
> -
> -		ret = clk_prepare_enable(tcu->clk);
> -		if (ret) {
> -			pr_crit("Unable to enable TCU clock\n");
> -			goto err_put_clk;
> +			/*
> +			 * Old device trees for some SoCs did not include the
> +			 * TCU clock because this driver (incorrectly) didn't
> +			 * use it. In this case we complain loudly and attempt
> +			 * to continue without the clock, which might work if
> +			 * booting with workarounds like "clk_ignore_unused".
> +			 */

Why not unconditionally enable it instead? Then it would boot without 
clk_ignore_unused.

Cheers,
-Paul

> +			if (tcu->soc_info->allow_missing_tcu_clk &&
> +			    PTR_ERR(tcu->clk) == -EINVAL) {
> +				pr_warn("TCU clock missing from device tree, please update your 
> device tree\n");
> +				tcu->clk = NULL;
> +			} else {
> +				pr_crit("Cannot get TCU clock from device tree\n");
> +				goto err_free_tcu;
> +			}
> +		} else {
> +			ret = clk_prepare_enable(tcu->clk);
> +			if (ret) {
> +				pr_crit("Unable to enable TCU clock\n");
> +				goto err_put_clk;
> +			}
>  		}
>  	}
> 
> @@ -432,10 +446,10 @@ static int __init ingenic_tcu_probe(struct 
> device_node *np)
>  			clk_hw_unregister(tcu->clocks->hws[i]);
>  	kfree(tcu->clocks);
>  err_clk_disable:
> -	if (tcu->soc_info->has_tcu_clk)
> +	if (tcu->clk)
>  		clk_disable_unprepare(tcu->clk);
>  err_put_clk:
> -	if (tcu->soc_info->has_tcu_clk)
> +	if (tcu->clk)
>  		clk_put(tcu->clk);
>  err_free_tcu:
>  	kfree(tcu);
> --
> 2.35.1
>