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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88391C61DA4 for ; Wed, 22 Feb 2023 16:39:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232385AbjBVQjK (ORCPT ); Wed, 22 Feb 2023 11:39:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232024AbjBVQjJ (ORCPT ); Wed, 22 Feb 2023 11:39:09 -0500 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6424F25E23; Wed, 22 Feb 2023 08:39:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=7LcgQyFEEIbtGtxl2T2txk9jkYZVDU3DC2iu/eSl9Kw=; b=0bUyJBeOu5kkiDdq09VZqOFzuk 9O25Mr39emOugDcEWoCt3by33YPM62wolEW515rZlpeUEyS0PMzgLINuDeGE0nAN/h4mVATtGqrdQ dULW7qIRTDapUCNUtrD1ufgG7LWmAzdtb19qZF1KUKBOemeJxwC15So2JYknaEWPYfT2Xc3SYCpR6 yKGqur28whPi95TQyZM3My380+URCSMvvRe6QSwB0r7txmR+ROvlXEBTaZeW9It4/470cVlgwbkkM R1HOMyZmN6R8JH+9Nu/PR2s3dT5SrUWvWDzARp1HuDIVviCi3GeV05lLhpjLJfgQdeJ2xYXU5eFTF V5IJtSiw==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:48318) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1pUs91-000799-Tr; Wed, 22 Feb 2023 16:39:03 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1pUs8z-0003LM-UA; Wed, 22 Feb 2023 16:39:01 +0000 Date: Wed, 22 Feb 2023 16:39:01 +0000 From: "Russell King (Oracle)" To: Marek Vasut Cc: netdev@vger.kernel.org, "David S. Miller" , Andrew Lunn , Arun Ramadoss , Eric Dumazet , Florian Fainelli , Jakub Kicinski , Paolo Abeni , UNGLinuxDriver@microchip.com, Vladimir Oltean , Woojung Huh , stable@vger.kernel.org Subject: Re: [PATCH] net: dsa: microchip: Fix gigabit set and get function for KSZ87xx Message-ID: References: <20230222031738.189025-1-marex@denx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Feb 22, 2023 at 05:30:43PM +0100, Marek Vasut wrote: > On 2/22/23 16:56, Russell King (Oracle) wrote: > > On Wed, Feb 22, 2023 at 04:10:33PM +0100, Marek Vasut wrote: > > > On 2/22/23 14:03, Russell King (Oracle) wrote: > > > > On Wed, Feb 22, 2023 at 12:50:07PM +0000, Russell King (Oracle) wrote: > > > > > On Wed, Feb 22, 2023 at 04:17:38AM +0100, Marek Vasut wrote: > > > > > > diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c > > > > > > index 729b36eeb2c46..7fc2155d93d6e 100644 > > > > > > --- a/drivers/net/dsa/microchip/ksz_common.c > > > > > > +++ b/drivers/net/dsa/microchip/ksz_common.c > > > > > > @@ -319,7 +319,7 @@ static const u16 ksz8795_regs[] = { > > > > > > [S_BROADCAST_CTRL] = 0x06, > > > > > > [S_MULTICAST_CTRL] = 0x04, > > > > > > [P_XMII_CTRL_0] = 0x06, > > > > > > - [P_XMII_CTRL_1] = 0x56, > > > > > > + [P_XMII_CTRL_1] = 0x06, > > > > > > > > > > Looking at this driver, I have to say that it looks utterly vile > > > > > from the point of view of being sure that it is correct, and I > > > > > think this patch illustrates why. > > > > > > > > > > You mention you're using a KSZ8794. This uses the ksz8795_regs > > > > > array, and ksz8_dev_ops. You claim this is about the P_GMII_1GBIT_M > > > > > bit, which is bit 6. > > > > > > > > > > This bit is accessed only by ksz_get_gbit() and ksz_set_gbit(). > > > > > > > > > > Firstly, ksz_set_gbit() is only called from ksz_port_set_xmii_speed(), > > > > > which is only called from ksz9477_phylink_mac_link_up(). This is only > > > > > referenced by ksz9477_dev_ops and lan937x_dev_ops, but not ksz8_dev_ops. > > > > > Therefore, ksz_set_gbit() is not called for KSZ8794. > > > > > > > > > > ksz_get_gbit() is only referenced by ksz9477.c in > > > > > ksz9477_get_interface(), called only by ksz9477_config_cpu_port(). > > > > > This is only referenced by ksz9477_dev_ops, but not ksz8_dev_ops. > > > > > > > > > > Therefore, my conclusion is that neither of the ksz_*_gbit() > > > > > functions are called on KSZ8794, and thus your change has no effect > > > > > on the driver's use of P_GMII_1GBIT_M - I think if you put some > > > > > debugging printk()s into both ksz_*_gbit() functions, it'll prove > > > > > that. > > > > > > > > > > There's other places that P_XMII_CTRL_1 is accessed - ksz_set_xmii() > > > > > and ksz_get_xmii(). These look at the P_MII_SEL_M, P_RGMII_ID_IG_ENABLE > > > > > and P_RGMII_ID_EG_ENABLE bits - bits 0, 1, 3 and 4. > > > > > > > > > > ksz_get_xmii() is only called by ksz9477_get_interface(), which we've > > > > > already looked at above as not being called. > > > > > > > > > > ksz_set_xmii() is only called by ksz_phylink_mac_config(), which is > > > > > always called irrespective of the KSZ chip. > > > > > > > > > > Now, let's look at functions that access P_XMII_CTRL_0. These are > > > > > ksz_set_100_10mbit() and ksz_duplex_flowctrl(). The former > > > > > accesses bit P_MII_100MBIT_M, which is bit 4. The latter looks at > > > > > bits 6, bit 5, and possibly bit 3 depending on the masks being used. > > > > > KSZ8795 uses ksz8795_masks, which omits bit 3, so bits 5 and 6. > > > > > Note... bit 6 is also P_GMII_1GBIT_M. So if ksz_duplex_flowctrl() > > > > > is ever called for the KSZ8795, then we have a situation where > > > > > the P_GMII_1GBIT_M will be manipulated. > > > > > > > > > > ksz_set_100_10mbit() is only called from ksz_port_set_xmii_speed(), > > > > > which we've established won't be called. > > > > > > > > > > ksz_duplex_flowctrl() is only called from ksz9477_phylink_mac_link_up() > > > > > which we've also established won't be called. > > > > > > > > > > So, as far as I can see, P_XMII_CTRL_0 won't be accessed on this > > > > > device. > > > > > > > > > > Now, what about other KSZ devices - I've analysed this for the KSZ8795, > > > > > but what about any of the others which use this register table? It > > > > > looks to me like those that use ksz8795_regs[] all use ksz8_dev_ops > > > > > and the same masks and bitvals, so they should be the same. > > > > > > > > > > That is a hell of a lot of work to prove that setting both > > > > > P_XMII_CTRL_0 and P_XMII_CTRL_1 to point at the same register is > > > > > in fact safe. Given the number of registers, the masks, and bitval > > > > > arrays, doing this to prove every combination and then analysing > > > > > the code is utterly impractical - and thus why I label this driver > > > > > as "vile". Is there really no better option to these register > > > > > arrays, bitval arrays and mask arrays - something that makes it > > > > > easier to review and prove correctness? > > > > > > > > > > I'm not going to give a reviewed-by for this, because... I could > > > > > have made a mistake in the above analysis given the vile nature > > > > > of this driver. > > > > > > > > However, I should add that - as a result of neither ksz_*_gbit() > > > > functions being used, I consider at least the subject line to be > > > > rather misleading! While it may be something that you spotted, > > > > I suspect the other bits that are actually written are more the > > > > issue you're fixing. > > > > > > Thank you for the lengthy review, I agree the driver and the register offset > > > calculation are hideous. > > > > > > However, I did spent quite a bit of time on it already and checked both > > > P_XMII_CTRL_0 and P_XMII_CTRL_1 mappings with printks and by dumping the > > > register values via regmap debugfs interface. > > > > > > Also note that KSZ8794 and KSZ8795 seem to be the same chip die, just > > > different package (the former has fewer ports) and different chip ID. > > > > It's not clear what you think of my review and whether you are going to > > take any action at all... So, let me try again... > > > > The fundamental question that my review raises was whether this gigabit > > bit is actually used, and your response remains silent on that point. > > > > As the gigabit bit is not actually used given the code structure, it > > is irrelevant for this commit, despite Is_Gbit being the thing that > > lead to the patch. > > > > Therefore, I believe that the patch description needs to be updated > > to state what the effective fix for this change is (which is to fix > > ksz_set_xmii()) rather than making it sound like it's fixing a wrong > > access for Is_Gbit. > > > > The reason I think this is important is that if we need to look back > > at the history, current description leads one to think that this > > change is about fixing the Is_Gbit bit - but that isn't used as the > > code stands. The effective change that this patch makes is to the > > only access the driver makes to this register in ksz_set_xmii(), > > and I think that needs to be explained as the primary reason for > > this patch. Fixing Is_Gbit seems to be merely incidental. > > On the hardware I use here, the P_XMII_CTRL_1 register ends up being > populated with all bits set, 0xff. Without this change, the driver writes to > non-existent register when it attempts to access P_XMII_CTRL_1 . Why is this so difficult? I'm *not* disagreeing with the patch. I'm disagreeing with your commit description. Okay, at this point, it seems I sadly have no option but to NAK this patch. Hopefully someone else can pick it up and give it a more reasonable commit description that properly describes the patch. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!