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=ham 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 337E0C43387 for ; Sun, 30 Dec 2018 03:29:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F3D9D21019 for ; Sun, 30 Dec 2018 03:29:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725941AbeL3D3I (ORCPT ); Sat, 29 Dec 2018 22:29:08 -0500 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:50362 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbeL3D3H (ORCPT ); Sat, 29 Dec 2018 22:29:07 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by kvm5.telegraphics.com.au (Postfix) with ESMTP id CF1AB28EDF; Sat, 29 Dec 2018 22:29:03 -0500 (EST) Date: Sun, 30 Dec 2018 14:28:56 +1100 (AEDT) From: Finn Thain To: Arnd Bergmann cc: Greg Kroah-Hartman , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Linux Kernel Mailing List , linux-m68k , linuxppc-dev Subject: Re: [PATCH v8 24/25] powerpc: Adopt nvram module for PPC64 In-Reply-To: Message-ID: References: <2fe2b8e6395aeacfafcbde590a50922d4e632189.1545784679.git.fthain@telegraphics.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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. -- > Arnd >