[llvmlinux] clang warning: implicit conversion in intel_ddi.c:1481

Ozgur o at zgur.org
Thu Feb 1 19:27:44 UTC 2018

01.02.2018, 21:03, "Greg KH" <greg at kroah.com>:
> 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

Hi Ozan,

why did you send e-mail to kernel development e-mail list?

>>  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


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