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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Linus Walleij , Alvin =?UTF-8?B?xaBpcHJhZ2E=?= , Yury Norov , Rasmus Villemoes , Russell King , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [net-next PATCH 04/10] bitfield.h: add FIELD_WIDTH() Message-ID: <20260404161211.47d8a05b@pumpkin> In-Reply-To: References: <20260331-realtek_forward-v1-0-44fb63033b7e@gmail.com> <20260331-realtek_forward-v1-4-44fb63033b7e@gmail.com> <20260402102717.5eb48393@pumpkin> <20260402232126.2e74631e@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 3 Apr 2026 11:09:30 -0300 Luiz Angelo Daros de Luca wrote: > Thanks David and Yuri, > > This patch was originally intended to reconstruct a value split across > multiple registers. Originally: > > vlan4k->member = > FIELD_GET(RTL8365MB_CVLAN_ENTRY_D0_MBR_MASK, data[0]) | > (FIELD_GET(RTL8365MB_CVLAN_ENTRY_D2_MBR_EXT_MASK, data[2]) > << FIELD_WIDTH(RTL8365MB_CVLAN_ENTRY_D0_MBR_MASK)); That calculation isn't even really correct. It is only right if the low bit of the last mask is set. I'm not a big fan of FIELD_GET/PREP - they have their use, but get overused. David > > However, as Yuri pointed out, I can use FIELD_PREP() to align the bits > into the final struct member without manual bitops. While less common, > this pattern is used elsewhere (e.g., drivers/clk/clk-lmk04832.c). The > updated approach would be: > > vlan4k->member = > FIELD_PREP(RTL8365MB_CVLAN_MBR_LO_MASK, > FIELD_GET(RTL8365MB_CVLAN_ENTRY_D0_MBR_MASK, > data[0])) | > FIELD_PREP(RTL8365MB_CVLAN_MBR_HI_MASK, > > FIELD_GET(RTL8365MB_CVLAN_ENTRY_D2_MBR_EXT_MASK, data[2])); > > If this use of FIELD_PREP is preferred, I will drop this FIELD_WIDTH > patch from the series as it would no longer have any users. > > Regards, > > Luiz >