linux-kernel - Re: [PATCH 09/20] clocksource/drivers/vf-pit: Register the clocksource from the driver

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Message-ID: <4101aa1a-efa3-418b-aa96-0157ffc7198f@linaro.org>
Date: Sat, 26 Jul 2025 21:37:43 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Ghennadi Procopciuc <ghennadi.procopciuc@....nxp.com>, tglx@...utronix.de
Cc: S32@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/20] clocksource/drivers/vf-pit: Register the
 clocksource from the driver

On 07/07/2025 14:02, Ghennadi Procopciuc wrote:
> On 7/5/2025 7:01 PM, Daniel Lezcano wrote:
> [...]
> 
>> +static u64 pit_timer_clocksource_read(struct clocksource *cs)
>> +{
>> +	struct pit_timer *pit = cs_to_pit(cs);
>> +
>> +	return ~(u64)readl(pit->clksrc_base + PITCVAL);
>> +}
> 
> The CVAL register is a 32-bit countdown timer. Casting its value to 64 bits before applying bitwise negation results in a 64-bit value where the upper 32 bits are always set. To avoid this, shouldn't the operations be reordered so that the bitwise negation is applied first to the 32-bit value, followed by casting the result to 64 bits?
> 

Yes, that's right

Good catch !

Thanks



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