linux-kernel - Re: [PATCH v1 1/2] clocksource/drivers/exynos_mct_v2: introduce Exynos MCT version 2 driver for next Exynos SoC

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Message-ID: <20211101052542.GA35671@perf>
Date:   Mon, 1 Nov 2021 14:25:42 +0900
From:   Youngmin Nam <youngmin.nam@...sung.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     daniel.lezcano@...aro.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, pullip.cho@...sung.com,
        hoony.yu@...sung.com, hajun.sung@...sung.com,
        myung-su.cha@...sung.com
Subject: Re: [PATCH v1 1/2] clocksource/drivers/exynos_mct_v2: introduce
 Exynos MCT version 2 driver for next Exynos SoC

On Wed, Oct 27, 2021 at 10:38:09AM +0200, Krzysztof Kozlowski wrote:
> On 21/10/2021 08:18, Youngmin Nam wrote:
> > Exynos MCT version 2 is composed of 1 FRC and 12 comparators.
> > The 12 comparators can produces interrupts independently,
> > so they can be used as local timer of each CPU.
> > 
> 
> ...
> 
> > +
> > +static void exynos_mct_comp_start(struct mct_clock_event_device *mevt,
> > +				  bool periodic, unsigned long cycles)
> > +{
> > +	unsigned int index = mevt->comp_index;
> > +	unsigned int comp_enable;
> > +	unsigned int loop_cnt = 0;
> > +
> > +	comp_enable = readl_relaxed(reg_base + EXYNOS_MCT_COMP_ENABLE(index));
> > +	if (comp_enable == MCT_COMP_ENABLE)
> > +		exynos_mct_comp_stop(mevt);
> > +
> > +	if (periodic)
> > +		writel_relaxed(MCT_COMP_CIRCULAR_MODE, reg_base + EXYNOS_MCT_COMP_MODE(index));
> > +
> > +	writel_relaxed(cycles, reg_base + EXYNOS_MCT_COMP_PERIOD(index));
> 
> This is unsigned long, so 64-bit on your platform. Use writeq_relaxed or
> handle it somehow.

Thanks for your review.
I checked again and data sheet of MCTv2 shows compartor period has 32-bit data width.
Once we write 32bit value to comp_period register, H/W will produce interrupt when increasing FRC
is the same with the value of "current FRC + comp_period".

> 
> 
> Best regards,
> Krzysztof
>