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Message-ID: <e23ebdd8-7fbe-435b-a850-0ef18a51b020@collabora.com>
Date: Tue, 19 Dec 2023 11:56:37 +0100
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Subject: Re: [PATCH v2] fix overflow in idle exit_latency
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To: Bo Ye <bo.ye@mediatek.com>, "Rafael J. Wysocki" <rafael@kernel.org>,
 Daniel Lezcano <daniel.lezcano@linaro.org>,
 Matthias Brugger <matthias.bgg@gmail.com>
Cc: yongdong.zhang@mediatek.com, C Cheng <C.Cheng@mediatek.com>,
 linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org
References: <20231219031444.91752-1-bo.ye@mediatek.com>
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
In-Reply-To: <20231219031444.91752-1-bo.ye@mediatek.com>
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Il 19/12/23 04:14, Bo Ye ha scritto:
> From: C Cheng <C.Cheng@mediatek.com>
> 
> In detail:
> 
> In C language, when you perform a multiplication operation, if
> both operands are of int type, the multiplication operation is
> performed on the int type, and then the result is converted to
> the target type. This means that if the product of int type
> multiplication exceeds the range that int type can represent,
>   an overflow will occur even if you store the result in a
> variable of int64_t type.
> 
> For a multiplication of two int values, it is better to use
> mul_u32_u32() rather than s->exit_latency_ns = s->exit_latency *
> NSEC_PER_USEC to avoid potential overflow happenning.
> 
> Signed-off-by: C Cheng <C.Cheng@mediatek.com>
> Signed-off-by: Bo Ye <bo.ye@mediatek.com>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>