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

From: Youngmin Nam <youngmin.nam@samsung.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Cc: daniel.lezcano@linaro.org, tglx@linutronix.de,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org, pullip.cho@samsung.com,
	hoony.yu@samsung.com, hajun.sung@samsung.com,
	myung-su.cha@samsung.com
Subject: Re: [PATCH v1 1/2] clocksource/drivers/exynos_mct_v2: introduce Exynos MCT version 2 driver for next Exynos SoC
Date: Mon, 1 Nov 2021 14:25:42 +0900	[thread overview]
Message-ID: <20211101052542.GA35671@perf> (raw)
In-Reply-To: <117dfec8-e417-642b-7647-9d17592826ad@canonical.com>

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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
> 

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