linux-kernel - Re: [RFC v6 01/23] clocksource: sh_cmt: compute rate before registration again

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Date:   Sat, 10 Sep 2016 14:56:47 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Nicolai Stange <nicstange@...il.com>
cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC v6 01/23] clocksource: sh_cmt: compute rate before registration
 again

On Fri, 9 Sep 2016, Nicolai Stange wrote:
> @@ -339,17 +339,14 @@ static int sh_cmt_enable(struct sh_cmt_channel *ch, unsigned long *rate)
>  	sh_cmt_start_stop_ch(ch, 0);
>  
>  	/* configure channel, periodic mode and maximum timeout */
> -	if (ch->cmt->info->width == 16) {
> -		*rate = clk_get_rate(ch->cmt->clk) / 512;
> +	if (ch->cmt->info->width == 16)
>  		sh_cmt_write_cmcsr(ch, SH_CMT16_CMCSR_CMIE |
>  				   SH_CMT16_CMCSR_CKS512);
> -	} else {
> -		*rate = clk_get_rate(ch->cmt->clk) / 8;
> +	else
>  		sh_cmt_write_cmcsr(ch, SH_CMT32_CMCSR_CMM |
>  				   SH_CMT32_CMCSR_CMTOUT_IE |
>  				   SH_CMT32_CMCSR_CMR_IRQ |
>  				   SH_CMT32_CMCSR_CKS_RCLK8);
> -	}

Removing the braces here is just wrong.

	if (foo)
		bar()
	else
		rab();

Is perfectly fine because the lack of braces tells that there are single
line statements in both branches.

	if (foo)
		bar(foo->something, foo->somemore, foo->other,
		    CONST);)
	else
		rab();

Is NOT. Simply because the pattern of a 'if ()' condition without braces
suggests a single line statement to follow. Then the reading flow stops
because there is more than one line. While:


	if (foo) {
		bar(foo->something, foo->somemore, foo->other,
		    CONST);)
	} else {
		rab();
	}

parses fine. With your 4 line single statement it's even worse.

>  	ret = sh_cmt_start(ch, FLAG_CLOCKSOURCE);
> -	if (!ret) {
> -		__clocksource_update_freq_hz(cs, ch->rate);
> +	if (!ret)
>  		ch->cs_enabled = true;
> -	}

This one is perfectly fine.

> @@ -824,6 +810,12 @@ static int sh_cmt_register_clockevent(struct sh_cmt_channel *ch,
>  	ced->suspend = sh_cmt_clock_event_suspend;
>  	ced->resume = sh_cmt_clock_event_resume;
>  
> +	/* TODO: calculate good shift from rate and counter bit width */
> +	ced->shift = 32;
> +	ced->mult = div_sc(ch->cmt->rate, NSEC_PER_SEC, ced->shift);


Errm. clockevents_calc_mult_shift()


> +	ced->max_delta_ns = clockevent_delta2ns(ch->max_match_value, ced);
> +	ced->min_delta_ns = clockevent_delta2ns(0x1f, ced);
> +
>  	dev_info(&ch->cmt->pdev->dev, "ch%u: used for clock events\n",
>  		 ch->index);
>  	clockevents_register_device(ced);

Thanks,

	tglx