linux-kernel - Re: [PATCH v2] drm/mediatek: fix uninitialized symbol

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Message-ID: <ecedbe0bd06a67654bc90421569ad6e6bd9ddfe7.camel@mediatek.com>
Date:   Thu, 3 Aug 2023 08:32:51 +0000
From:   Nancy Lin (林欣螢) <Nancy.Lin@...iatek.com>
To:     CK Hu (胡俊光) <ck.hu@...iatek.com>,
        "fshao@...omium.org" <fshao@...omium.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Singo Chang (張興國) 
        <Singo.Chang@...iatek.com>,
        "chunkuang.hu@...nel.org" <chunkuang.hu@...nel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "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>,
        "clang-built-linux@...glegroups.com" 
        <clang-built-linux@...glegroups.com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Subject: Re: [PATCH v2] drm/mediatek: fix uninitialized symbol

Hi CK and Fei,

Thanks for the review.

On Thu, 2023-07-20 at 07:52 +0000, CK Hu (胡俊光) wrote:
> Hi, Fei:
> 
> On Mon, 2023-07-17 at 11:59 +0800, Fei Shao wrote:
> >  	 
> > External email : Please do not click links or open attachments
> > until
> > you have verified the sender or the content.
> >  Hi CK,
> > 
> > On Fri, Jul 14, 2023 at 5:27 PM CK Hu (胡俊光) <ck.hu@...iatek.com>
> > wrote:
> > > 
> > > Hi, Nancy:
> > > 
> > > On Fri, 2023-04-21 at 10:16 +0800, Nancy.Lin wrote:
> > 
> > snip
> > > 
> > > In line 566, the statement is
> > > 
> > > if (nodo) {
> > >         comp_pdev = ...
> > > }
> > > 
> > > The comment says that only ovl_adaptoer has no device node, so
> > > the
> > > checking should be
> > > 
> > > if (type != MTK_DISP_OVL_ADAPTOR) {
> > >         comp_pdev = ...
> > > }
> > > 
> > > and later it would return when type = MTK_DISP_OVL_ADAPTOR,
> > > so there would be no problem of uninitialized symbol.
> > 
> > That sounds fair, but IIUC what Nancy tries to resolve here is the
> > false-positive Smatch warning.
> > How about this: given the `if (node)` block was exclusively added
> > for
> > ovl_adaptor in [1], plus the init function will immediately return
> > after that in this case, it should be safe to do the following
> > 
> > ```
> > /* Not all drm components have a DTS device node... */
> > if (node == NULL)
> >     return 0;
> > 
> > comp_pdev = of_find_device_by_node(node);
> > ...
> > 
> > if (type == MTK_DISP_AAL ||
> > ...
> > ```
> > 
> > which is equivalent to adding a `node == NULL` check before [1].
> > This should suppress the Smatch warning because `comp_pdev` will be
> > (again) unconditionally assigned to something, and the `type ==
> > MTK_DISP_OVL_ADAPTOR` line can be dropped also (optional?).
> 
> This solution also looks good to me.
> 
> Regards,
> CK
> 
I will send the next version of modifications based on your
suggestions.

Thanks,
Nancy

> > 
> > [1]: commit 0d9eee9118b7 ("drm/mediatek: Add drm ovl_adaptor sub
> > driver for MT8195")
> > 
> > Regards,
> > Fei