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Wed, 8 Oct 2025 20:24:32 +0200 (CEST) Message-ID: <205478244873d09cad5b77bd887f6a836c31c7ec.camel@collabora.com> Subject: Re: [PATCH 00/25] media: v4l2-mem2mem: Reduce cargo-cult From: Nicolas Dufresne To: Laurent Pinchart , linux-media@vger.kernel.org, linux-mediatek@lists.infradead.org, imx@lists.linux.dev, linux-amlogic@lists.infradead.org, linux-renesas-soc@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org Cc: Matthew Majewski , Mirela Rabulea , Jacek Anaszewski , Michael Tretter , Devarsh Thakkar , Uwe =?ISO-8859-1?Q?Kleine-K=F6nig?= , AngeloGioacchino Del Regno , Martin Blumenstingl , Alexandre Torgue , Philipp Zabel , Arnd Bergmann , Sylwester Nawrocki , Ming Qian , Pengutronix Kernel Team , Kieran Bingham , Nathan Chancellor , Sascha Hauer , Hans Verkuil , Mikhail Ulyanov , Kevin Hilman , Xavier Roumegue , Shuah Khan , Andrzej Pietrasiewicz , Tiffany Lin , Zhou Peng , Dikshita Agarwal , Vikash Garodia , Yunfei Dong , Ezequiel Garcia , Neil Armstrong , Jiasheng Jiang , Shawn Guo , =?UTF-8?Q?=C5=81ukasz?= Stelmach , Abhinav Kumar , Heiko Stuebner , Benoit Parrot , Andrew-CT Chen , Geert Uytterhoeven , Magnus Damm , Sebastian Fricke , Maxime Coquelin , Jacob Chen , Bin Liu , Matthias Brugger , Fabio Estevam , Jerome Brunet , Bryan O'Donoghue Date: Wed, 08 Oct 2025 14:24:30 -0400 In-Reply-To: <20251008175052.19925-1-laurent.pinchart@ideasonboard.com> References: <20251008175052.19925-1-laurent.pinchart@ideasonboard.com> Autocrypt: addr=nicolas.dufresne@collabora.com; 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boundary="===============7748363189015318142==" Sender: "linux-amlogic" Errors-To: linux-amlogic-bounces+linux-amlogic=archiver.kernel.org@lists.infradead.org --===============7748363189015318142== Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-LjFEnUafECFwApd/yAvu" --=-LjFEnUafECFwApd/yAvu Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi, Le mercredi 08 octobre 2025 =C3=A0 20:50 +0300, Laurent Pinchart a =C3=A9cr= it=C2=A0: > Hello, >=20 > The v4l2_m2m_get_vq() function never returns NULL, but many mem2mem > drivers still check its return value and consider NULL as an error. This > may have originated a long time ago from valid checks when > v4l2_m2m_get_vq() could return NULL, with drivers then just copying the > checks. This series attempts to stop the cargo-cult behaviour. >=20 > Patch 01/25 starts by explicitly stating in kerneldoc that the > v4l2_m2m_get_vq() function never returns NULL. All the other patches > drop NULL checks from drivers. >=20 > I have carefully checked all patched locations in all drivers. They fall > in 3 categories: >=20 > - Checks in the VIDIOC_G_FMT, VIDIOC_TRY_FMT and VIDIOC_S_FMT handlers: > =C2=A0 Those may have been added to ensure that the format type has a val= id > =C2=A0 value, but that is ensured by the V4L2 ioctl core before calling t= he > =C2=A0 handlers. The checks can be dropped without a need to replace them > =C2=A0 with proper type checks. >=20 > - Checks in the VIDIOC_S_SELECTION handler: The only location where this > =C2=A0 is performed has an explicit type check, so the NULL check can als= o be > =C2=A0 dropped. >=20 > - Checks in other locations where the type parameter to the > =C2=A0 v4l2_m2m_get_vq() function is hardcoded: The hardcoded type is val= id, > =C2=A0 so the NULL check can't have been meant to check the type. It can = also > =C2=A0 be removed. >=20 > There's no dependency between any of those patches so they can be merged > in any order. >=20 > Laurent Pinchart (25): > =C2=A0 media: v4l2-mem2mem: Document that v4l2_m2m_get_vq() never returns > =C2=A0=C2=A0=C2=A0 NULL > =C2=A0 media: allgro-dvt: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: meson-g2d: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: amphion: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: coda: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: imagination: e5010: Drop unneeded v4l2_m2m_get_vq() NULL ch= eck > =C2=A0 media: m2m-deinterlace: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: mediatek: jpeg: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: mediatek: vcodec: Drop unneeded v4l2_m2m_get_vq() NULL chec= k > =C2=A0 media: dw100: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: imx-jpeg: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: imx-pxp: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: nxp: imx8-isi: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: mx2_emmaprp: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: qcom: iris: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: qcom: venus: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: renesas: fdp1: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: rcar_jpu: Drop unneeded v4l2_m2m_get_vq() NULL check Why not "renesas: jpu" to match the fdp1 patch naming ? > =C2=A0 media: platform: rga: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: samsung: s5p-g2d: Drop unneeded v4l2_m2m_get_vq() NULL chec= k > =C2=A0 media: samsung: s5p-jpeg: Drop unneeded v4l2_m2m_get_vq() NULL che= ck > =C2=A0 media: stm32: dma2d: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: ti: vpe: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: vicodec: Drop unneeded v4l2_m2m_get_vq() NULL check > =C2=A0 media: vim2m: Drop unneeded v4l2_m2m_get_vq() NULL check I reviewed the list and it seems complete to me. Nicolas >=20 > =C2=A0drivers/media/platform/allegro-dvt/allegro-core.c=C2=A0=C2=A0=C2=A0= |=C2=A0 2 -- > =C2=A0drivers/media/platform/amlogic/meson-ge2d/ge2d.c=C2=A0=C2=A0=C2=A0= =C2=A0 |=C2=A0 5 ----- > =C2=A0drivers/media/platform/amphion/vdec.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0drivers/media/platform/amphion/venc.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0.../media/platform/chips-media/coda/coda-common.c=C2=A0=C2=A0=C2=A0= |=C2=A0 4 ---- > =C2=A0drivers/media/platform/imagination/e5010-jpeg-enc.c=C2=A0 |=C2=A0 4= ---- > =C2=A0drivers/media/platform/m2m-deinterlace.c=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 7 ------- > =C2=A0drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c |=C2=A0 7 ----= --- > =C2=A0.../mediatek/vcodec/decoder/mtk_vcodec_dec.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 7 ------- > =C2=A0.../vcodec/decoder/vdec/vdec_av1_req_lat_if.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0.../vcodec/decoder/vdec/vdec_vp9_req_lat_if.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0.../mediatek/vcodec/encoder/mtk_vcodec_enc.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 8 -------- > =C2=A0drivers/media/platform/nxp/dw100/dw100.c=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 7 ------- > =C2=A0drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 |=C2=A0 4 ---- > =C2=A0drivers/media/platform/nxp/imx-pxp.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 = 7 ------- > =C2=A0drivers/media/platform/nxp/imx8-isi/imx8-isi-m2m.c=C2=A0=C2=A0 |=C2= =A0 2 -- > =C2=A0drivers/media/platform/nxp/mx2_emmaprp.c=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 7 ------- > =C2=A0drivers/media/platform/qcom/iris/iris_vdec.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0drivers/media/platform/qcom/venus/vdec.c=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0drivers/media/platform/qcom/venus/venc.c=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 2 -- > =C2=A0drivers/media/platform/renesas/rcar_fdp1.c=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 3 --- > =C2=A0drivers/media/platform/renesas/rcar_jpu.c=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 8 -------- > =C2=A0drivers/media/platform/rockchip/rga/rga.c=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 4 ---- > =C2=A0drivers/media/platform/samsung/s5p-g2d/g2d.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 4 ---- > =C2=A0drivers/media/platform/samsung/s5p-jpeg/jpeg-core.c=C2=A0 |=C2=A0 7= ------- > =C2=A0drivers/media/platform/st/stm32/dma2d/dma2d.c=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 |=C2=A0 5 ----- > =C2=A0drivers/media/platform/ti/vpe/vpe.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |= =C2=A0 7 ------- > =C2=A0drivers/media/test-drivers/vicodec/vicodec-core.c=C2=A0=C2=A0=C2=A0= |=C2=A0 7 ------- > =C2=A0drivers/media/test-drivers/vim2m.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= | 12 ------------ > =C2=A0drivers/media/v4l2-core/v4l2-mem2mem.c=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 12 +----------- > =C2=A0include/media/v4l2-mem2mem.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 3 +++ > =C2=A031 files changed, 4 insertions(+), 153 deletions(-) >=20 >=20 > base-commit: e5f0a698b34ed76002dc5cff3804a61c80233a7a --=-LjFEnUafECFwApd/yAvu Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCaOasXgAKCRDZQZRRKWBy 9F8oAP92tHDSFRd6mdp01gSe1GDFGPRn1q4aOR2d4zEl8W2BoQEAuXK4NGidjdie sOQmoarDKx/ErFatR3/qQmk9d+ZaGAY= =Bmyy -----END PGP SIGNATURE----- --=-LjFEnUafECFwApd/yAvu-- --===============7748363189015318142== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-amlogic mailing list linux-amlogic@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-amlogic --===============7748363189015318142==--