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[209.85.221.182]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-866941da3fdsm1549787241.25.2025.02.03.05.59.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Feb 2025 05:59:49 -0800 (PST) Received: by mail-vk1-f182.google.com with SMTP id 71dfb90a1353d-518ae5060d4so1388081e0c.0; Mon, 03 Feb 2025 05:59:48 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCUCSxPdtewQcOQ0VqH6KbxR4AJHf9AWvwOdRbLTbvQjRiAZ4FpuZD5vIUmLA1S5L+pEJdteSv/vOmkN@vger.kernel.org, AJvYcCUHuzVuJTMpt0LQKeVDHJ1VtblVA/jQAqbWjUWIRKIAuAyMlzBNOZ/n6K0qxfK3H0yghOkGUzfpxLj+nA==@vger.kernel.org, AJvYcCUZWFTVihvApMJKLl3n2E9mazFs5hQcdPJnyLYEnO0kTePafT0VDFcesNs+EowedR+CcfkxEFzF4dg=@vger.kernel.org, AJvYcCUl+wcql7GU+jy8A7Dvt2aY/XyP/TwLPAXwO9xOPEQ/OFOMj8i3HBHDoMKuZDAnPGp2HKUaKVISae34fkFw@vger.kernel.org, AJvYcCV/NESNNuh7EgpaWW3U7NQXZ8TenqvtEB3nzQdJP0gppFbLr7BKmXebhvwfM1xasbU1m7lxPWX5uxaf4K+y@vger.kernel.org, AJvYcCWC0XUNHF1VlrFHkUNsacVF3cs7Ach9FCtZrUL+/sL865CKb7gH5rsQRDTFY2MrD+KjCMJAulaNj4aUiVM=@vger.kernel.org, AJvYcCWWdCymXHv2toYAg5XNDIfLqTNh8zJ8w2ClBk1asRJsOYRuIbavqezhrOlfMYhCYUSWlReR4F0bs1YGMfCqAGy3SHI=@vger.kernel.org X-Received: by 2002:a05:6122:1990:b0:51c:aa1a:2b5b with SMTP id 71dfb90a1353d-51e9e3fdc44mr15881808e0c.4.1738591188554; Mon, 03 Feb 2025 05:59:48 -0800 (PST) Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <1824412519cb8791ab428065116927ee7b77cf35.1738329459.git.geert+renesas@glider.be> <74cab7d1ec31e7531cdda0f1eb47acdebd5c8d3f.camel@sipsolutions.net> <45920591-e1d6-4337-a906-35bb5319836c@wanadoo.fr> In-Reply-To: <45920591-e1d6-4337-a906-35bb5319836c@wanadoo.fr> From: Geert Uytterhoeven Date: Mon, 3 Feb 2025 14:59:36 +0100 X-Gmail-Original-Message-ID: X-Gm-Features: AWEUYZkxzrXQCnvoDXR55r9qIi7LTjZDYDZYK_OEJibEwCDu5alOHeJTYjGkvIg Message-ID: Subject: Re: [PATCH treewide v2 1/3] bitfield: Add non-constant field_{prep,get}() helpers To: Vincent Mailhol Cc: Johannes Berg , Yury Norov , linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-renesas-soc@vger.kernel.org, linux-crypto@vger.kernel.org, qat-linux@intel.com, linux-gpio@vger.kernel.org, linux-aspeed@lists.ozlabs.org, linux-iio@vger.kernel.org, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, Michael Turquette , Stephen Boyd , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , Giovanni Cabiddu , Herbert Xu , "David S . Miller" , Linus Walleij , Bartosz Golaszewski , Joel Stanley , Andrew Jeffery , Crt Mori , Jonathan Cameron , Lars-Peter Clausen , Jacky Huang , Shan-Chun Hung , Rasmus Villemoes , Jaroslav Kysela , Takashi Iwai , Jakub Kicinski , Alex Elder Content-Type: text/plain; charset="UTF-8" Hi Vincent, On Mon, 3 Feb 2025 at 14:37, Vincent Mailhol wrote: > On 03/02/2025 at 16:44, Johannes Berg wrote: > > On Sun, 2025-02-02 at 12:53 -0500, Yury Norov wrote: > >>> Instead of creating another variant for > >>> non-constant bitfields, wouldn't it be better to make the existing macro > >>> accept both? > >> > >> Yes, it would definitely be better IMO. > > > > On the flip side, there have been discussions in the past (though I > > think not all, if any, on the list(s)) about the argument order. Since > > the value is typically not a constant, requiring the mask to be a > > constant has ensured that the argument order isn't as easily mixed up as > > otherwise. > > If this is a concern, then it can be checked with: > > BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask) && > __builtin_constant_p(_val), > _pfx "mask is not constant"); > > It means that we forbid FIELD_PREP(non_const_mask, const_val) but allow > any other combination. Even that case looks valid to me. Actually there is already such a user in drivers/iio/temperature/mlx90614.c: ret |= field_prep(chip_info->fir_config_mask, MLX90614_CONST_FIR); So if you want enhanced safety, having both the safer/const upper-case variants and the less-safe/non-const lower-case variants makes sense. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds