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Peter Anvin" , Andy Lutomirski , Jonathan Cameron , David Lechner , Nuno =?iso-8859-1?Q?S=E1?= , Andy Shevchenko , Ping-Ke Shih , Richard Cochran , Andrew Lunn , "David S. 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?yHwJFZ5TtBao77wuWSrGy3a1I98HwauB0CHUwUML2lp3J1rciU74jGs3bOFs?= =?us-ascii?Q?yuivJzNLZ7yHKB3zKiak0LIJbLHzZQFytsP/hEXryzxk96PVdgEMv9VGZ9DC?= =?us-ascii?Q?cINHp89C/PMFCFnLl0rOeJQDTRheM33/EEabe3QcLPKuCo4b9qiKtfMuNIjE?= =?us-ascii?Q?Tt23DJs60qZ0nh5+c65v6cJMc7+di7rEaIzCD3Of2tIXfQCEzycZUhDXCQxx?= =?us-ascii?Q?rkfU1t7sbwFu8D+sihCs54LizirPAO05ZT93BZ4fXUcsuZoRs9aBsvAph6Aw?= =?us-ascii?Q?xj30mSkxFBzXiR34P7bpEmNJuAdK3dNCrBd/WT+wuESKzx3CTJUFbNs7l0kj?= =?us-ascii?Q?a6Cv1R2LLWLRRrwrPrMS19wnrmAuegRmoHQ5lCQ0rOEk/k1kM5O44mqjr+5o?= =?us-ascii?Q?AdyN3WKtbKU0tflZUhhtS9+DVE7O4fMJl+7xlF4wlBNhlIYbAraynjf8xlix?= =?us-ascii?Q?q3yxHhAHfQIqrUZ6FyT2mpNvPeagaHOhzqIT5eA49L1CXv6b/gmnS1nJYZkS?= =?us-ascii?Q?pxLZl9jPaFogVnqg0ZSJ7dQzDY8drRuaLDUC/V1Sq2Ol1+WAhS5pFKFRlPir?= =?us-ascii?Q?dYTT1QvA7uDvdbWp2AgXpVUDO4vBgDWDeRfJ1wtwrOtiC1CFcopZqWnLJXWk?= =?us-ascii?Q?ej1ko2HDxsD37eGmynWgo4U5uJ698WB+P8QVxbuCFp65SktST8hmQg6OqSj3?= =?us-ascii?Q?MsGZiLFApAAHDiW/UYvlNNC8MFallGP+fehowQAkSzfSIu1jL7+rsU/H1JPm?= =?us-ascii?Q?s11ku+Lel3HodbQ5/TjrdGDxNG3vQV44aZPLUuEJRq6ciw2RSoKNrnW6I0X5?= =?us-ascii?Q?IU/JYDh79UqaT9nBkdmCGo8POsqsFYoCyoV/p3IqC2ES9Q4mAblMYnXoFPQ4?= =?us-ascii?Q?QS3I0GRNdgTQCZET4WtM1JlfzWcc74yEf5uOioikGDz2BJVzcpP5zxBP1dkb?= =?us-ascii?Q?HHKsV+lPhlT+zgzWZwfsJHPQAIeLJCoM+NwGxBlT4AfoyX+bQXDYkb0PTprr?= =?us-ascii?Q?76TKl1VWcSYokUCLAyIhlc5h3Jy1AoHdsooNpt6BVUWadnz/AAoxgDc3BWRq?= =?us-ascii?Q?x3pS/EoQDywy8HrdPUeSFI4KJJsZl0h69OLgM8M/Q8sShGtpO5LLKlL0IqW5?= =?us-ascii?Q?Lgw/8Unm7q8bV14ugzNFCL76tziLU+hojm532OaHlHuIXGGWCoJAdkZjM2ii?= =?us-ascii?Q?l+Xf5XY3CmAB1juJXaaHFJ0Ol86+Qy3jDSsW69kHRHbDXjeNcyCOfhc/Z8x/?= =?us-ascii?Q?FQczWzE8hqLU7RfS5Vuro+J5Q04LpxX/3nuic0Ye6YNfamzqjn4re8BEMBhC?= =?us-ascii?Q?aVCglEmCoadzLJJUBWwfpyYNo8vRuEbmvBXxdhn6yeuxeAeAUM/0IIbmGVZK?= =?us-ascii?Q?2WvtAj+XgIiGy5xGt9p6P5V+c4iNYu2Nu802ts5CMv1UD5W8WQDaMnsl/lgf?= =?us-ascii?Q?3se0uLXdNNCWXXLJO0s3ZCp8ofgJITDBtPDop0q2rJrQfGxYkOQIrZsEnolO?= =?us-ascii?Q?usV6FjRqGFnswJ0XvhqebFBVisw036LxjMr7kb8esTndTsdLqw3PBabYITHv?= =?us-ascii?Q?Xu4sLFXzvAYmQNycgkzleWK2RyUMki0B9JVEj3aut59iWpM+oT06w6X6/jIf?= =?us-ascii?Q?Yk9/W1MeZp4FUzdVF3bhufNp+w8ANQJxOB6F47Cqsz83jeYXWuOyKSYqOf+e?= =?us-ascii?Q?dw8cRSmY95+44x6FVHnrEGXNW9RxacPHUbSnZZTkAxOkhCGX1jhoYXSDzVyZ?= =?us-ascii?Q?r8TZZuGbgub+JMwmLuNdrnvbLoiAkfWS73yNWlBqoZz5raVXQp2+?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 757bf9c5-3e53-4f96-18d6-08de9f05f101 X-MS-Exchange-CrossTenant-AuthSource: CY8PR12MB8300.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Apr 2026 17:55:00.1875 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: vRF5JMAbfqelYiSL29Lh/qYmW4kLW3nOsgmrCfKcf5gOGHVBrkVEi31veRSjTemNVYtB27MfKINzdpC2L2rcEg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4074 On Mon, Apr 20, 2026 at 01:19:40PM +0200, Peter Zijlstra wrote: > On Fri, Apr 17, 2026 at 01:36:12PM -0400, Yury Norov wrote: > > The bitfields are designed in assumption that fields contain unsigned > > integer values, thus extracting the values from the field implies > > zero-extending. > > > > Some drivers need to sign-extend their fields, and currently do it like: > > > > dc_re += sign_extend32(FIELD_GET(0xfff000, tmp), 11); > > dc_im += sign_extend32(FIELD_GET(0xfff, tmp), 11); > > > > It's error-prone because it relies on user to provide the correct > > index of the most significant bit and proper 32 vs 64 function flavor. > > > > Thus, introduce a FIELD_GET_SIGNED() macro, which is the more > > convenient and compiles (on x86_64) to just a couple instructions: > > shl and sar. > > > > Signed-off-by: Yury Norov > > --- > > include/linux/bitfield.h | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > > > > diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h > > index 54aeeef1f0ec..35ef63972810 100644 > > --- a/include/linux/bitfield.h > > +++ b/include/linux/bitfield.h > > @@ -178,6 +178,22 @@ > > __FIELD_GET(_mask, _reg, "FIELD_GET: "); \ > > }) > > > > +/** > > + * FIELD_GET_SIGNED() - extract a signed bitfield element > > + * @mask: shifted mask defining the field's length and position > > + * @reg: value of entire bitfield > > + * > > + * Returns the sign-extended field specified by @_mask from the > > + * bitfield passed in as @_reg by masking and shifting it down. > > + */ > > +#define FIELD_GET_SIGNED(mask, reg) \ > > + ({ \ > > + __BF_FIELD_CHECK(mask, reg, 0U, "FIELD_GET_SIGNED: "); \ > > + ((__signed_scalar_typeof(mask))((long long)(reg) << \ > > + __builtin_clzll(mask) >> (__builtin_clzll(mask) + \ > > + __builtin_ctzll(mask))));\ > > + }) > > IIRC clz is count-leading-zeros and ctz is count-trailing-zeros. Most of > the other FIELD things use __bf_shf() which is defined in terms of ffs - > 1 (which is another way of writing ctz). > > So how about you start by redefining __bf_shf() in ctz, and then add > another helper for the clz and write the thing something like: > > ((long long)(reg) << __bf_clz(mask)) >> (__bf_clz(mask) + __bf_shf(mask)); So... I like the shorter form, but whatever we add in the bitfield.h - we'll have to support it. For example, __bf_shf() wasn't intended to be used outsize of the header, thus double underscored. But there's over 100 external users now. And to make it worse, it's broken for GCC 14 and earlier: https://lore.kernel.org/all/20260409-field-prep-fix-v1-1-f0e9ae64f63c@imgtec.com/ So needs to get fixed. The bitfield.h has two __bf macros: __bf_shf() and __bf_cast_unsigned(). They are thin wrappers, but after all do something with the corresponding builtins output. The __bf_cls() would be a pure renaming. I'm OK with that, but some people don't: https://lore.kernel.org/all/20260303182845.250bb2de@kernel.org/ That's why I didn't make FIELD_GET_SIGNED() implementation looking nicer. If you strongly prefer the shorter version, I can do that in v2. > Also, since the order of the shifts is rather important, I think it > makes sense to add this extra pair of (), even when not strictly needed, > just to make it easier to read. Sure, will do.