linux-kernel - Re: clang warning: implicit conversion in intel

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Message-ID: <20180201180240.GA28042@kroah.com>
Date:   Thu, 1 Feb 2018 19:02:40 +0100
From:   Greg KH <greg@...ah.com>
To:     Ozan Alpay <ozyalpy@...il.com>
Cc:     Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>, sil2review@...ts.osadl.org,
        kernelnewbies@...nelnewbies.org, David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        llvmlinux@...ts.linuxfoundation.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        lukas.bulwahn@...il.com
Subject: Re: clang warning: implicit conversion in intel_ddi.c:1481

On Thu, Feb 01, 2018 at 06:33:30PM +0100, Ozan Alpay wrote:
> Dear Rodrigo Vivi, Ville Syrjälä,
> 
> My name is Ozan Alpay, and I am a student mentored by Lukas Bulwahn. We 
> intend to use static analysis tools on the kernel source to identify, 
> analyze and report issues. As a very first step, we are looking into 
> clang compiler warnings and will then move to more sophisticated tools. 
> 
> When compiling Linux 4.15 with clang, we have discovered that your commit 
> 2952cd6fb4cc ("drm/i915: Let's use more enum intel_dpll_id pll_id.") 
> introduced the following warning:
> 
> drivers/gpu/drm/i915/intel_ddi.c:1481:30: warning: implicit conversion from enumeration type 'enum port' to different enumeration type 'enum intel_dpll_id' [-Wenum-conversion] 
> 	enum intel_dpll_id pll_id = port;
> 
> To reproduce it, you can compile Linux 4.15 with clang with this command: 
> 
> make HOSTCC=clang-5.0 defconfig && make -j32 HOSTCC=clang-5.0 CC=clang-5.0
> 
> If you don't have clang installed in your system, you can use this simple 
> docker setup to compile the kernel with clang:
> 
> wget https://raw.githubusercontent.com/bulwahn/linux-kernel-analysis/master/docker/kernel-clang/Dockerfile && \
> docker build -t kernel-clang . && \
> docker run -v <your kernel source directory>:/linux/ kernel-clang /bin/sh -c "cd linux && make CC=clang-5.0 clean && make HOSTCC=clang-5.0 defconfig && make -j32 HOSTCC=clang-5.0 CC=clang-5.0"
>  
> While we were doing our analysis on 4.15, we noticed that you already 
> resolved this warning on linux-next with your work in commit bb911536f07e 
> ("drm/i915: Eliminate pll->state usage from bxt_calc_pll_link()"). So, 
> since it is resolved on linux-next and we expect that this commit will be 
> merged in the merge window for 4.16, there is probably nothing further to 
> do.
> 
> Linux 4.15 is shipped with this clang warning, but we don't see the 
> crucial need to provide a backport commit to the stable branch for 4.15. 
> We just wanted to inform you about our analysis of this clang warning. 
> Ultimately the final call if you would like to address this clang warning 
> in 4.15 is yours.

Note, I have not taken "clang warning fixes" for stable kernel updates
in the past, and I doubt I will in the future, unless the tree "builds
clean" with clang.  If it eventually gets there, then yes, I will do
that.

Note, if you are going to email this out to everyone who fixes a warning
message, you might want to reconsider it.  That's going to be a lot of
work, and for people who have already fixed an issue, it's kind of
pointless to just remind them of work they have done in the past, right?

What is the goal of these types of emails?

thanks,

greg k-h