linux-kernel - Re: [PATCH 2/2] phy: mediatek: hdmi: mt8195: fix wrong pll calculus

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Message-ID: <52440231-bbcc-48f6-fe47-a554cade8d73@collabora.com>
Date:   Fri, 14 Apr 2023 12:34:35 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Guillaume Ranquet <granquet@...libre.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-phy@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] phy: mediatek: hdmi: mt8195: fix wrong pll calculus

Il 13/04/23 14:46, Guillaume Ranquet ha scritto:
> The clock rate calculus in mtk_hdmi_pll_calc() was wrong when it has
> been replaced by 'div_u64'.
> 
> Fix the issue by multiplying the values in the denominator instead of
> dividing them.
> 
> Fixes: 45810d486bb44 ("phy: mediatek: add support for phy-mtk-hdmi-mt8195")
> Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> ---
>   drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> index e10da6c4147e..5e84b294a43e 100644
> --- a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> +++ b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> @@ -271,7 +271,7 @@ static int mtk_hdmi_pll_calc(struct mtk_hdmi_phy *hdmi_phy, struct clk_hw *hw,
>   	 * [32,24] 9bit integer, [23,0]:24bit fraction
>   	 */
>   	pcw = div_u64(((u64)ns_hdmipll_ck) << PCW_DECIMAL_WIDTH,
> -		      da_hdmitx21_ref_ck / PLL_FBKDIV_HS3);
> +		      da_hdmitx21_ref_ck * PLL_FBKDIV_HS3);

How did that even work?!?!?!? Because ... it worked, I did test it. Bah!
Luck was on your side :-P

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