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

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Message-ID: <CABnWg9v+DXatKqUkwDZBRxivtg869SocPGtHibtFNr7tnyVggg@mail.gmail.com>
Date:   Fri, 14 Apr 2023 05:52:57 -0700
From:   Guillaume Ranquet <granquet@...libre.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.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>
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

On Fri, 14 Apr 2023 12:31, AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>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
>

Hi Angelo,
I was maybe a bit too quick on fixing this that way.
Anyway it doesn't change a thing as mtk_hdmi_pll_set_hw() eitheir
returns 0 or -EINVAL.
But I agree that the logic is dubious and propagating the return value
is the right thing
to do.

I see that Arnd and Tom posted versions that you might prefer:

https://lore.kernel.org/linux-phy/20230414075842.4006164-1-arnd@kernel.org/
https://lore.kernel.org/linux-phy/20230414122253.3171524-1-trix@redhat.com/

Thx,
Guillaume.

>	ret = mtk_hdmi_pll_set_hw(....)
>	if (ret)
>		return ret;
>
>	return 0;
>
>
>Regards,
>Angelo