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Mon, 30 Mar 2026 16:17:28 +0200 (CEST) Message-ID: Subject: Re: [PATCH 1/4] media: rkvdec: Introduce a global bitwriter helper From: Nicolas Dufresne To: Detlev Casanova , Ezequiel Garcia , Mauro Carvalho Chehab , Heiko Stuebner , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Jonas Karlman Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-rockchip@lists.infradead.org, linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev, kernel@collabora.com Date: Mon, 30 Mar 2026 10:17:26 -0400 In-Reply-To: <20260327-rkvdec-use-bitwriter-v1-1-982cf872b590@collabora.com> References: <20260327-rkvdec-use-bitwriter-v1-0-982cf872b590@collabora.com> <20260327-rkvdec-use-bitwriter-v1-1-982cf872b590@collabora.com> Autocrypt: addr=nicolas.dufresne@collabora.com; prefer-encrypt=mutual; keydata=mDMEaCN2ixYJKwYBBAHaRw8BAQdAM0EHepTful3JOIzcPv6ekHOenE1u0vDG1gdHFrChD /e0J05pY29sYXMgRHVmcmVzbmUgPG5pY29sYXNAbmR1ZnJlc25lLmNhPoicBBMWCgBEAhsDBQsJCA cCAiICBhUKCQgLAgQWAgMBAh4HAheABQkJZfd1FiEE7w1SgRXEw8IaBG8S2UGUUSlgcvQFAmibrjo CGQEACgkQ2UGUUSlgcvQlQwD/RjpU1SZYcKG6pnfnQ8ivgtTkGDRUJ8gP3fK7+XUjRNIA/iXfhXMN abIWxO2oCXKf3TdD7aQ4070KO6zSxIcxgNQFtDFOaWNvbGFzIER1ZnJlc25lIDxuaWNvbGFzLmR1Z nJlc25lQGNvbGxhYm9yYS5jb20+iJkEExYKAEECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4 AWIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCaCyyxgUJCWX3dQAKCRDZQZRRKWBy9ARJAP96pFmLffZ smBUpkyVBfFAf+zq6BJt769R0al3kHvUKdgD9G7KAHuioxD2v6SX7idpIazjzx8b8rfzwTWyOQWHC AAS0LU5pY29sYXMgRHVmcmVzbmUgPG5pY29sYXMuZHVmcmVzbmVAZ21haWwuY29tPoiZBBMWCgBBF iEE7w1SgRXEw8IaBG8S2UGUUSlgcvQFAmibrGYCGwMFCQll93UFCwkIBwICIgIGFQoJCAsCBBYCAw ECHgcCF4AACgkQ2UGUUSlgcvRObgD/YnQjfi4+L8f4fI7p1pPMTwRTcaRdy6aqkKEmKsCArzQBAK8 bRLv9QjuqsE6oQZra/RB4widZPvphs78H0P6NmpIJ Organization: Collabora Canada Content-Type: multipart/signed; micalg="pgp-sha512"; protocol="application/pgp-signature"; boundary="=-yBgy0sQvaoJVzhLo4NBc" User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260330_071735_668544_1FA1E646 X-CRM114-Status: GOOD ( 21.89 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org --=-yBgy0sQvaoJVzhLo4NBc Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Le vendredi 27 mars 2026 =C3=A0 11:16 -0400, Detlev Casanova a =C3=A9crit= =C2=A0: > The use of structures with bitfields is good when the values are > somewhat aligned. > More mis-alignement means that compilers need to do more gymanstics > to edit the fields values. >=20 > Some cases have been reported with CLang on specific architectures > like armhf and hexagon, where the compiler would allocate a bigger > local stack than needed or even completely freeze during compilation. >=20 > Some fixes have been provided to ease the issues, but the real fix > here is to use a bitwriter instead of heavily unaligned bitfields. >=20 > This is a preparation commit to provide a global bitwriter interface > for the whole driver. >=20 > Signed-off-by: Detlev Casanova > --- > =C2=A0drivers/media/platform/rockchip/rkvdec/Makefile=C2=A0=C2=A0=C2=A0 |= =C2=A0 1 + > =C2=A0.../platform/rockchip/rkvdec/rkvdec-bitwriter.c=C2=A0=C2=A0=C2=A0 |= 30 ++++++++++++++++++++++ > =C2=A0.../platform/rockchip/rkvdec/rkvdec-bitwriter.h=C2=A0=C2=A0=C2=A0 |= 25 ++++++++++++++++++ > =C2=A03 files changed, 56 insertions(+) >=20 > diff --git a/drivers/media/platform/rockchip/rkvdec/Makefile b/drivers/me= dia/platform/rockchip/rkvdec/Makefile > index e629d571e4d8..11e2122bcbbf 100644 > --- a/drivers/media/platform/rockchip/rkvdec/Makefile > +++ b/drivers/media/platform/rockchip/rkvdec/Makefile > @@ -2,6 +2,7 @@ obj-$(CONFIG_VIDEO_ROCKCHIP_VDEC) +=3D rockchip-vdec.o > =C2=A0 > =C2=A0rockchip-vdec-y +=3D \ > =C2=A0 =C2=A0=C2=A0 rkvdec.o \ > + =C2=A0=C2=A0 rkvdec-bitwriter.o \ Its just one function, with 10 lines of code, can we inline it in the heade= r and drop the object ? > =C2=A0 =C2=A0=C2=A0 rkvdec-cabac.o \ > =C2=A0 =C2=A0=C2=A0 rkvdec-h264.o \ > =C2=A0 =C2=A0=C2=A0 rkvdec-h264-common.o \ > diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-bitwriter.c b/= drivers/media/platform/rockchip/rkvdec/rkvdec-bitwriter.c > new file mode 100644 > index 000000000000..673ebb89002b > --- /dev/null > +++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-bitwriter.c > @@ -0,0 +1,30 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Rockchip Video Decoder bit writer > + * > + * Copyright (C) 2026 Collabora, Ltd. > + *=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Detlev Casanova > + * Copyright (C) 2019 Collabora, Ltd. > + * Boris Brezillon > + */ > + > +#include > +#include > + > +#include "rkvdec-bitwriter.h" > + > +void rkvdec_set_bw_field(u32 *buf, struct rkvdec_bw_field field, u32 val= ue) > +{ > + u8 bit =3D field.offset % 32; > + u16 word =3D field.offset / 32; > + u64 mask =3D GENMASK_ULL(bit + field.len - 1, bit); > + u64 val =3D ((u64)value << bit) & mask; > + > + buf[word] &=3D ~mask; > + buf[word] |=3D val; > + if (bit + field.len > 32) { > + buf[word + 1] &=3D ~(mask >> 32); > + buf[word + 1] |=3D val >> 32; > + } > +} > + > diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-bitwriter.h b/= drivers/media/platform/rockchip/rkvdec/rkvdec-bitwriter.h > new file mode 100644 > index 000000000000..44154f1ebc65 > --- /dev/null > +++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-bitwriter.h > @@ -0,0 +1,25 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Rockchip Video Decoder bit writer > + * > + * Copyright (C) 2026 Collabora, Ltd. > + *=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Detlev Casanova > + * Copyright (C) 2019 Collabora, Ltd. > + * Boris Brezillon > + */ > + > +#ifndef RKVDEC_BIT_WRITER_H_ > +#define RKVDEC_BIT_WRITER_H_ > + > +#include > + > +struct rkvdec_bw_field { > + u16 offset; > + u8 len; > +}; > + > +#define BW_FIELD(_offset, _len) ((struct rkvdec_bw_field){ _offset, _len= }) > + > +void rkvdec_set_bw_field(u32 *buf, struct rkvdec_bw_field field, u32 val= ue); > + > +#endif /* RKVDEC_BIT_WRITER_H_ */ --=-yBgy0sQvaoJVzhLo4NBc Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTvDVKBFcTDwhoEbxLZQZRRKWBy9AUCacqF9gAKCRDZQZRRKWBy 9NNPAP9m/C7TMvFwXyQT8rK+UCGFvzuLY32by5+QAQwsH+fP4wEAoC19z0cPX+2k voSc2sk6B5FI6fzPOJXJX9z9XlPO0go= =/Y4+ -----END PGP SIGNATURE----- --=-yBgy0sQvaoJVzhLo4NBc--