linux-kernel - Re: [PATCH] clocksource/drivers/sh_cmt: Make sure channel clock supply is enabled

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Message-ID: <X+ie4/6dt+ZJ8qH2@wyvern>
Date:   Sun, 27 Dec 2020 15:49:07 +0100
From:   Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Magnus Damm <damm@...nsource.se>,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clocksource/drivers/sh_cmt: Make sure channel clock
 supply is enabled

Hi Geert,

Thanks for your patch.

On 2020-12-10 20:46:48 +0100, Geert Uytterhoeven wrote:
> The Renesas Compare Match Timer 0 and 1 (CMT0/1) variants have a
> register to control the clock supply to the individual channels.
> Currently the driver does not touch this register, and relies on the
> documented initial value, which has the clock supply enabled for all
> channels present.
> 
> However, when Linux starts on the APE6-EVM development board, only the
> clock supply to the first CMT1 channel is enabled.  Hence the first
> channel (used as a clockevent) works, while the second channel (used as
> a clocksource) does not.  Note that the default system clocksource is
> the Cortex-A15 architectured timer, and the user needs to manually
> switch to the CMT1 clocksource to trigger the broken behavior.
> 
> Fix this by removing the fragile dependency on implicit reset and/or
> boot loader state, and by enabling the clock supply explicitly for all
> channels used instead.  This requires postponing the clk_disable() call,
> else the timer's registers cannot be accessed in sh_cmt_setup_channel().
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

> ---
> Tested on R-Mobile APE6, R-Car M2-W, and R-Car H3 ES2.0.
> ---
>  drivers/clocksource/sh_cmt.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clocksource/sh_cmt.c b/drivers/clocksource/sh_cmt.c
> index e258230d432c0002..c98f8851fd680454 100644
> --- a/drivers/clocksource/sh_cmt.c
> +++ b/drivers/clocksource/sh_cmt.c
> @@ -235,6 +235,8 @@ static const struct sh_cmt_info sh_cmt_info[] = {
>  #define CMCNT 1 /* channel register */
>  #define CMCOR 2 /* channel register */
>  
> +#define CMCLKE	0x1000	/* CLK Enable Register (R-Car Gen2) */
> +
>  static inline u32 sh_cmt_read_cmstr(struct sh_cmt_channel *ch)
>  {
>  	if (ch->iostart)
> @@ -853,6 +855,7 @@ static int sh_cmt_setup_channel(struct sh_cmt_channel *ch, unsigned int index,
>  				unsigned int hwidx, bool clockevent,
>  				bool clocksource, struct sh_cmt_device *cmt)
>  {
> +	u32 value;
>  	int ret;
>  
>  	/* Skip unused channels. */
> @@ -882,6 +885,11 @@ static int sh_cmt_setup_channel(struct sh_cmt_channel *ch, unsigned int index,
>  		ch->iostart = cmt->mapbase + ch->hwidx * 0x100;
>  		ch->ioctrl = ch->iostart + 0x10;
>  		ch->timer_bit = 0;
> +
> +		/* Enable the clock supply to the channel */
> +		value = ioread32(cmt->mapbase + CMCLKE);
> +		value |= BIT(hwidx);
> +		iowrite32(value, cmt->mapbase + CMCLKE);
>  		break;
>  	}
>  
> @@ -1014,12 +1022,10 @@ static int sh_cmt_setup(struct sh_cmt_device *cmt, struct platform_device *pdev)
>  	else
>  		cmt->rate = clk_get_rate(cmt->clk) / 8;
>  
> -	clk_disable(cmt->clk);
> -
>  	/* Map the memory resource(s). */
>  	ret = sh_cmt_map_memory(cmt);
>  	if (ret < 0)
> -		goto err_clk_unprepare;
> +		goto err_clk_disable;
>  
>  	/* Allocate and setup the channels. */
>  	cmt->num_channels = hweight8(cmt->hw_channels);
> @@ -1047,6 +1053,8 @@ static int sh_cmt_setup(struct sh_cmt_device *cmt, struct platform_device *pdev)
>  		mask &= ~(1 << hwidx);
>  	}
>  
> +	clk_disable(cmt->clk);
> +
>  	platform_set_drvdata(pdev, cmt);
>  
>  	return 0;
> @@ -1054,6 +1062,8 @@ static int sh_cmt_setup(struct sh_cmt_device *cmt, struct platform_device *pdev)
>  err_unmap:
>  	kfree(cmt->channels);
>  	iounmap(cmt->mapbase);
> +err_clk_disable:
> +	clk_disable(cmt->clk);
>  err_clk_unprepare:
>  	clk_unprepare(cmt->clk);
>  err_clk_put:
> -- 
> 2.25.1
> 

-- 
Regards,
Niklas Söderlund