linux-kernel - Re: [PATCH 3/3] media: mediatek: vcodedc: Fix Wcast-function-type-strict warnings

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Date: Sun, 4 Feb 2024 13:55:49 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Nícolas F. R. A. Prado <nfraprado@...labora.com>
Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Ricardo Ribalda <ribalda@...omium.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>, Mike Isely <isely@...ox.com>,
	Tiffany Lin <tiffany.lin@...iatek.com>,
	Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
	Yunfei Dong <yunfei.dong@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 3/3] media: mediatek: vcodedc: Fix
 Wcast-function-type-strict warnings

On Fri, Feb 02, 2024 at 03:15:46PM -0500, Nícolas F. R. A. Prado wrote:
> On Fri, Feb 02, 2024 at 01:58:05PM +0100, AngeloGioacchino Del Regno wrote:
> > Il 01/02/24 23:25, Sami Tolvanen ha scritto:
> > > On Thu, Feb 1, 2024 at 10:17 PM Nathan Chancellor <nathan@...nel.org> wrote:
> > > > 
> > > > On Sun, Jan 28, 2024 at 02:12:22AM +0000, Ricardo Ribalda wrote:
> > > > > Building with LLVM=1 throws the following warning:
> > > > > drivers/media/platform/mediatek/vcodec/common/mtk_vcodec_fw_vpu.c:38:32: warning: cast from 'mtk_vcodec_ipi_handler' (aka 'void (*)(void *, unsigned int, void *)') to 'ipi_handler_t' (aka 'void (*)(const void *, unsigned int, void *)') converts to incompatible function type [-Wcast-function-type-strict]
> > > > > 
> > > > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > > 
> > > > I am not positive because I don't have any hardware to test this driver
> > > > but I suspect this patch is just hiding the warning without actually
> > > > addressing the issue that it is pointing out.
> > > 
> > > Agreed, this won't fix the issue. The correct solution is to drop the
> > > cast and change the handler type to match the pointer type (i.e. use
> > > const void* for the first argument).
> > > 
> > 
> > Even though I agree that the correct solution is to change the handler's type,
> > I think that having a test on the actual hardware done is still valuable.
> > 
> > We scheduled a job on KernelCI to test this commit on our integration kernel,
> > you'll get results for ChromeOS' tast decoders (MT8195 only) and Fluster tests
> > on MT8183/8186/8192/8195.
> > 
> > 
> > The results should be available in a couple of hours here, relative to
> > commit `49955a84129dbe1f94fedf729690efcf28513828` on our tree:
> > https://chromeos.kernelci.org/job/collabora-chromeos-kernel/branch/for-kernelci/
> > 
> > P.S.: If they don't, feel free to ping me or Nicolas (added to the loop) about it.
> 
> Hi,
> 
> the results are available at 
> 
> https://chromeos.kernelci.org/test/job/collabora-chromeos-kernel/branch/for-kernelci/kernel/v6.8-rc2-3109-g49955a84129d/
> 
> (You need to type "decoder" into the search bar to limit the results to only the
> decoder tests)
> 
> The only regressions I see are due to infrastructure error or broken test
> unrelated to this change (v4l2-decoder-conformance-h264-frext test on
> MT8195-Tomato, and cros-tast-decoder-v4l2-sl-h264 test on MT8183-Juniper)
> 
> Otherwise, all platforms (MT8183/8186/8192/8195) and video codecs
> (VP8/VP9/H264/H265/AV1) seem unaffected.
> 
> Note that these are GCC builds.

Thank you for running the tests to make sure this series does not
regress anything. If possible, it would be good to try and build with
LLVM and enable kernel Control Flow Integrity (kCFI, CONFIG_CFI_CLANG)
to see if my theory that this is currently broken is correct. I have
prebuilt LLVM toolchains on kernel.org but if it is too much of a
hassle, I would not worry about it.

https://mirrors.edge.kernel.org/pub/tools/llvm/

Cheers,
Nathan