linux-kernel - Re: [PATCH v3 3/4] drm/mediatek: Add casting before assign

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Date:   Thu, 22 Jun 2023 08:02:07 +0000
From:   Jason-JH Lin (林睿祥) 
        <Jason-JH.Lin@...iatek.com>
To:     "amergnat@...libre.com" <amergnat@...libre.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
CC:     "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        Johnson Wang (王聖鑫) 
        <Johnson.Wang@...iatek.com>,
        Jason-ch Chen (陳建豪) 
        <Jason-ch.Chen@...iatek.com>,
        Shawn Sung (宋孝謙) 
        <Shawn.Sung@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>
Subject: Re: [PATCH v3 3/4] drm/mediatek: Add casting before assign

Hi Alexandre,

Thanks for the reviews.

On Wed, 2023-06-21 at 14:34 +0200, Alexandre Mergnat wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  
> 
> On 21/06/2023 12:22, Jason-JH.Lin wrote:
> > 1. Add casting before assign to avoid the unintentional integer
> >     overflow or unintended sign extension.
> > 2. Add a int varriable for multiplier calculation instead of
> calculating
> >     different types multiplier with dma_addr_t varriable directly.
> > 
> > Fixes: 1a64a7aff8da ("drm/mediatek: Fix cursor plane no update")
> > Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> > ---
> >   drivers/gpu/drm/mediatek/mtk_drm_gem.c   |  3 ++-
> >   drivers/gpu/drm/mediatek/mtk_drm_plane.c | 22 +++++++++++++----
> -----
> >   2 files changed, 15 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > index a25b28d3ee90..da087d74612d 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> > @@ -121,7 +121,8 @@ int mtk_drm_gem_dumb_create(struct drm_file
> *file_priv, struct drm_device *dev,
> >   int ret;
> >   
> >   args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
> > -args->size = args->pitch * args->height;
> > +args->size = args->pitch;
> > +args->size *= args->height;
> >   
> >   mtk_gem = mtk_drm_gem_create(dev, args->size, false);
> >   if (IS_ERR(mtk_gem))
> > diff --git a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> > index 31f9420aff6f..1cd41454d545 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> > @@ -145,6 +145,7 @@ static void mtk_plane_update_new_state(struct
> drm_plane_state *new_state,
> >   dma_addr_t addr;
> >   dma_addr_t hdr_addr = 0;
> >   unsigned int hdr_pitch = 0;
> > +int offset;
> 
> I agree with Angelo, please set offset as unsigned.
> 
I think offset should be unsigned, but since src.x1 and src.y1 are
'int'. That means 'unsigned int' offset will be very big when src.x1 or
src.y1 is negative.
So I just use 'int' for offset here.

Regards,
Jason-JH.Lin

> >   
> >   gem = fb->obj[0];
> >   mtk_gem = to_mtk_gem_obj(gem);
> > @@ -154,8 +155,10 @@ static void mtk_plane_update_new_state(struct
> drm_plane_state *new_state,
> >   modifier = fb->modifier;
> >   
> >   if (modifier == DRM_FORMAT_MOD_LINEAR) {
> > -addr += (new_state->src.x1 >> 16) * fb->format->cpp[0];
> > -addr += (new_state->src.y1 >> 16) * pitch;
> > +offset = (new_state->src.x1 >> 16) * fb->format->cpp[0];
> > +addr += offset;
> > +offset = (new_state->src.y1 >> 16) * pitch;
> > +addr += offset;
>