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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 7EE11C433E0 for ; Mon, 25 May 2020 02:46:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6410D20899 for ; Mon, 25 May 2020 02:46:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388721AbgEYCq5 (ORCPT ); Sun, 24 May 2020 22:46:57 -0400 Received: from foss.arm.com ([217.140.110.172]:35100 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388136AbgEYCq4 (ORCPT ); Sun, 24 May 2020 22:46:56 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 16EB531B; Sun, 24 May 2020 19:46:56 -0700 (PDT) Received: from [192.168.122.166] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B46FD3F305; Sun, 24 May 2020 19:46:55 -0700 (PDT) Subject: Re: [RFC 01/11] net: phy: Don't report success if devices weren't found To: Russell King - ARM Linux admin Cc: netdev@vger.kernel.org, davem@davemloft.net, andrew@lunn.ch, f.fainelli@gmail.com, hkallweit1@gmail.com, madalin.bucur@oss.nxp.com, calvin.johnson@oss.nxp.com, linux-kernel@vger.kernel.org References: <20200522213059.1535892-1-jeremy.linton@arm.com> <20200522213059.1535892-2-jeremy.linton@arm.com> <20200523182054.GW1551@shell.armlinux.org.uk> From: Jeremy Linton Message-ID: Date: Sun, 24 May 2020 21:46:55 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200523182054.GW1551@shell.armlinux.org.uk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Thanks for taking a look at this. On 5/23/20 1:20 PM, Russell King - ARM Linux admin wrote: > On Fri, May 22, 2020 at 04:30:49PM -0500, Jeremy Linton wrote: >> C45 devices are to return 0 for registers they haven't >> implemented. This means in theory we can terminate the >> device search loop without finding any MMDs. In that >> case we want to immediately return indicating that >> nothing was found rather than continuing to probe >> and falling into the success state at the bottom. > > This is a little confusing when you read this comment: > > /* If mostly Fs, there is no device there, > * then let's continue to probe more, as some > * 10G PHYs have zero Devices In package, > * e.g. Cortina CS4315/CS4340 PHY. > */ > > Since it appears to be talking about the case of a PHY where *devs will > be zero. However, tracking down the original submission, it seems this > is not the case at all, and the comment is grossly misleading. > > It seems these PHYs only report a valid data in the Devices In Package > registers for devad=0 - it has nothing to do with a zero Devices In > Package. Yes, this ended up being my understanding of this commit, and is part of my justification for starting the devices search at the reserved address 0 rather than 1. > > Can I suggest that this comment is fixed while we're changing the code > to explicitly reject this "zero Devices In package" so that it's not > confusing? Its probably better to kill it in 5/11 with a mention that we are starting at a reserved address? OTOH, I'm a bit concerned that reading at 0 as the first address will cause problems because the original code was only triggering it after a read returning 0xFFFFFFFF at a valid MMD address. It does simplify/clarify the loop though. If it weren't for this 0 read, I would have tried to avoid some of the additional MMD reserved addresses.