linux-kernel - Re: [PATCH v2] drm:sprd: Correct left shift operator evaluating constant expression

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Message-ID: <gdbbczffcnhhzkka5znerr5usy6qn2iu5grzzr7tifb3wozimw@jeemooscmnrk>
Date: Sat, 9 Nov 2024 13:33:27 +0000
From: Karan Sanghavi <karansanghvi98@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Orson Zhai <orsonzhai@...il.com>, Baolin Wang <baolin.wang@...ux.alibaba.com>, 
	Chunyan Zhang <zhang.lyra@...il.com>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2] drm:sprd: Correct left shift operator evaluating
 constant expression

On Sat, Nov 09, 2024 at 09:27:36AM +0200, Dmitry Baryshkov wrote:
> On Fri, Nov 08, 2024 at 05:11:25PM +0000, Karan Sanghavi wrote:
> > The left shift operation followed by a mask with 0xf will
> > always result in 0. To correctly evaluate the expression for
> > the bitwise OR operation, use a right shift instead.
> > 
> > Reported by Coverity Scan CID: 1511468
> > 
> > Fixes: 1c66496b1391 ("drm/sprd: add Unisoc's drm mipi dsi&dphy driver")
> > 
> > Reviewed-by: Chunyan Zhang <zhang.lyra@...il.com>
> > Signed-off-by: Karan Sanghavi <karansanghvi98@...il.com>
> 
> Please drop the empty line between tags.
> 
> Also see Documentation/process/stable-kernel-rules.rst
> 
Sure will go through that.
> > ---
> > Coverity Scan Message:
> > CID 1511468: (#1 of 1): Wrong operator used (CONSTANT_EXPRESSION_RESULT)
> > operator_confusion: (pll->kint << 4) & 15 is always 0 regardless of the 
> > values of its operands. This occurs as the bitwise second operand of "|"
> 
> Is there any kind of a public link for the report? Should there be a Closes: tag?
>
https://scan7.scan.coverity.com/#/project-view/51975/11354?selectedIssue=1511468

This is the link for coverity scan report. 

Should I add this link in the Closes tag? 

> > ---
> > Changes in v2:
> > - Added the fixes tag
> > - Link to v1: https://lore.kernel.org/r/20241105-coverity1511468wrongoperator-v1-1-06c7513c3efc@gmail.com
> > ---
> >  drivers/gpu/drm/sprd/megacores_pll.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/sprd/megacores_pll.c b/drivers/gpu/drm/sprd/megacores_pll.c
> > index 3091dfdc11e3..43c10a5fc441 100644
> > --- a/drivers/gpu/drm/sprd/megacores_pll.c
> > +++ b/drivers/gpu/drm/sprd/megacores_pll.c
> > @@ -94,7 +94,7 @@ static void dphy_set_pll_reg(struct dphy_pll *pll, struct regmap *regmap)
> >  	reg_val[3] = pll->vco_band | (pll->sdm_en << 1) | (pll->refin << 2);
> >  	reg_val[4] = pll->kint >> 12;
> >  	reg_val[5] = pll->kint >> 4;
> > -	reg_val[6] = pll->out_sel | ((pll->kint << 4) & 0xf);
> > +	reg_val[6] = pll->out_sel | ((pll->kint >> 4) & 0xf);
> >  	reg_val[7] = 1 << 4;
> >  	reg_val[8] = pll->det_delay;
> >  
> > 
> > ---
> > base-commit: 81983758430957d9a5cb3333fe324fd70cf63e7e
> > change-id: 20241105-coverity1511468wrongoperator-20130bcd4240
> > 
> > Best regards,
> > -- 
> > Karan Sanghavi <karansanghvi98@...il.com>
> > 
> 
> -- 
> With best wishes
> Dmitry
Thank you,
Karan.