linux-kernel - Re: [PATCH 1/2] phy: mediatek: hdmi: mt8195: fix uninitialized variable usage in pll

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Date:   Fri, 14 Apr 2023 12:31:47 +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,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH 1/2] phy: mediatek: hdmi: mt8195: fix uninitialized
 variable usage in pll_calc

Il 13/04/23 14:46, Guillaume Ranquet ha scritto:
> The ret variable in mtk_hdmi_pll_calc() was used unitialized as reported
> by the kernel test robot.
> 
> Fix the issue by removing the variable altogether and testing out the
> return value of mtk_hdmi_pll_set_hw()
> 
> Fixes: 45810d486bb44 ("phy: mediatek: add support for phy-mtk-hdmi-mt8195")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
> ---
>   drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c | 7 +++----
>   1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> index abfc077fb0a8..e10da6c4147e 100644
> --- a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> +++ b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> @@ -213,7 +213,7 @@ static int mtk_hdmi_pll_calc(struct mtk_hdmi_phy *hdmi_phy, struct clk_hw *hw,
>   	u64 tmds_clk, pixel_clk, da_hdmitx21_ref_ck, ns_hdmipll_ck, pcw;
>   	u8 txpredivs[4] = { 2, 4, 6, 12 };
>   	u32 fbkdiv_low;
> -	int i, ret;
> +	int i;
>   
>   	pixel_clk = rate;
>   	tmds_clk = pixel_clk;
> @@ -292,10 +292,9 @@ static int mtk_hdmi_pll_calc(struct mtk_hdmi_phy *hdmi_phy, struct clk_hw *hw,
>   	if (!(digital_div <= 32 && digital_div >= 1))
>   		return -EINVAL;
>   
> -	mtk_hdmi_pll_set_hw(hw, PLL_PREDIV, fbkdiv_high, fbkdiv_low,
> +	if (mtk_hdmi_pll_set_hw(hw, PLL_PREDIV, fbkdiv_high, fbkdiv_low,
>   			    PLL_FBKDIV_HS3, posdiv1, posdiv2, txprediv,
> -			    txposdiv, digital_div);
> -	if (ret)
> +			    txposdiv, digital_div))
>   		return -EINVAL;
>   

I don't get why we're returning -EINVAL unconditionally in the first place, here.

Function mtk_hdmi_pll_set_hw() should return zero or a negative error number: in
that case, the previous *intention* was fine, so this should be

	ret = mtk_hdmi_pll_set_hw(....)
	if (ret)
		return ret;

	return 0;


Regards,
Angelo