From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 06347C43387 for ; Mon, 31 Dec 2018 12:37:24 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4FB6520828 for ; Mon, 31 Dec 2018 12:37:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4FB6520828 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arndb.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 43Sxf90r0HzDqJq for ; Mon, 31 Dec 2018 23:37:21 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=arndb.de Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=gmail.com (client-ip=209.85.160.194; helo=mail-qt1-f194.google.com; envelope-from=arndbergmann@gmail.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=arndb.de Received: from mail-qt1-f194.google.com (mail-qt1-f194.google.com [209.85.160.194]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 43SxYR0KMPzDqKM for ; Mon, 31 Dec 2018 23:33:14 +1100 (AEDT) Received: by mail-qt1-f194.google.com with SMTP id u47so24563082qtj.6 for ; Mon, 31 Dec 2018 04:33:14 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=RwU2Y+gpTZt+nue9fhxVSylTa7plk4FrzInK4LqoluI=; b=ror+Wa3+a48p+2js3zL12C85IVM+CwICwinP5gSlH4Grb/8hwlT5NM3fsW+LVE9duu bqzQb7+2Vijq1sosipk8y/S/2T7mvLWOpvXRgMURJGTAGxdr8VcFbo8Dju70SR4QPMuA /VqdRF/oAQzMXl5uCSr0DlyXJibrAnRdPSy7YMpDpgYNBJ90e/zT/bFG3OWRkQPKPb+r dzgrtVty2FYImsBGoHsLWVN/pu8ZDEgcUJKqJr7Yr9y36BzDzToWU8lqRTFB5UMjCHzF bBs8F97+KQ2vh6ewN2Dl8BCQSpvbIYb0WvLuI4W37vKfXp90jzRpR8vU9RBxK57Quq+z XFtQ== X-Gm-Message-State: AJcUukdWDlq6UGPEUpcGTGDOEt79+abs9TMqChr9KjovCBvwiRrTf5F8 CY779eGaKgLQJthmAitptpm/rt533Eq2Mr0OK3I= X-Google-Smtp-Source: ALg8bN4TD/GbypKBpOh5YRDFPzr2bnm3gxPGhwf/NOqhuWWtVExcUwllgVZc0JW3lX4qvLgT1gWHihXC91JJj95wCKA= X-Received: by 2002:a0c:f50c:: with SMTP id j12mr35192233qvm.149.1546259592841; Mon, 31 Dec 2018 04:33:12 -0800 (PST) MIME-Version: 1.0 References: <2fe2b8e6395aeacfafcbde590a50922d4e632189.1545784679.git.fthain@telegraphics.com.au> In-Reply-To: From: Arnd Bergmann Date: Mon, 31 Dec 2018 13:32:56 +0100 Message-ID: Subject: Re: [PATCH v8 24/25] powerpc: Adopt nvram module for PPC64 To: Finn Thain Content-Type: text/plain; charset="UTF-8" X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Greg Kroah-Hartman , Linux Kernel Mailing List , linux-m68k , Paul Mackerras , linuxppc-dev Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sun, Dec 30, 2018 at 4:29 AM Finn Thain wrote: > > On Sat, 29 Dec 2018, Arnd Bergmann wrote: > > > On Wed, Dec 26, 2018 at 1:43 AM Finn Thain wrote: > > > > > +static ssize_t ppc_nvram_get_size(void) > > > +{ > > > + if (ppc_md.nvram_size) > > > + return ppc_md.nvram_size(); > > > + return -ENODEV; > > > +} > > > > > +const struct nvram_ops arch_nvram_ops = { > > > + .read = ppc_nvram_read, > > > + .write = ppc_nvram_write, > > > + .get_size = ppc_nvram_get_size, > > > + .sync = ppc_nvram_sync, > > > +}; > > > > Coming back to this after my comment on the m68k side, I notice that > > there is now a double indirection through function pointers. Have you > > considered completely removing the operations from ppc_md instead by > > having multiple copies of nvram_ops? > > > > I considered a few alternatives. I figured that it was refactoring that > could be deferred, as it would be confined to arch/powerpc. I was more > interested in the cross-platform API. Fair enough. > > With the current method, it does seem odd to have a single > > per-architecture instance of the exported structure containing function > > pointers. This doesn't give us the flexibility of having multiple copies > > in the kernel the way that ppc_md does, but it adds overhead compared to > > simply exporting the functions directly. > > > > You're right, there is overhead here. > > With a bit of auditing, wrappers like the one you quoted (which merely > checks whether or not a ppc_md method is implemented) could surely be > avoided. > > The arch_nvram_ops methods are supposed to optional (that is, they are > allowed to be NULL). > > We could call exactly the same function pointers though either ppc_md or > arch_nvram_ops. That would avoid the double indirection. I think you can have a 'const' structure in the __ro_after_init section, so without changing anything else, powerpc could just copy the function pointers from ppc_md into the arch_nvram_ops at early init time, which should ideally simplify your implementation as well. Arnd