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mx.microsoft.com 1; spf=pass smtp.mailfrom=topicproducts.com; dmarc=pass action=none header.from=topic.nl; dkim=pass header.d=topic.nl; arc=none Authentication-Results-Original: vger.kernel.org; dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=none action=none header.from=topic.nl; Received: from DB8PR04MB6523.eurprd04.prod.outlook.com (2603:10a6:10:10f::26) by DB8PR04MB5673.eurprd04.prod.outlook.com (2603:10a6:10:a6::26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3805.16; Thu, 28 Jan 2021 08:45:42 +0000 Received: from DB8PR04MB6523.eurprd04.prod.outlook.com ([fe80::792a:b2ef:ed50:a1a2]) by DB8PR04MB6523.eurprd04.prod.outlook.com ([fe80::792a:b2ef:ed50:a1a2%4]) with mapi id 15.20.3784.017; Thu, 28 Jan 2021 08:45:42 +0000 Subject: Re: [PATCH] net: mdiobus: Prevent spike on MDIO bus reset signal To: Andrew Lunn CC: netdev@vger.kernel.org, "David S. Miller" , Heiner Kallweit , Jakub Kicinski , Russell King , linux-kernel@vger.kernel.org References: <20210126073337.20393-1-mike.looijmans@topic.nl> <1b153bce-a66a-45ee-a5c6-963ea6fb1c82.949ef384-8293-46b8-903f-40a477c056ae.7228ddf2-6794-42a0-8b0b-3821446cdb40@emailsignatures365.codetwo.com> <1b153bce-a66a-45ee-a5c6-963ea6fb1c82.0d2bd5fa-15cc-4b27-b94e-83614f9e5b38.7855d092-e2c3-4ba5-a029-2a0bbce637e1@emailsignatures365.codetwo.com> From: Mike Looijmans Organization: TOPIC Message-ID: <956acc58-6ec8-c3d5-1310-7305c3b5a471@topic.nl> Date: Thu, 28 Jan 2021 09:45:41 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-CA Content-Transfer-Encoding: quoted-printable X-Originating-IP: [81.173.50.109] X-ClientProxiedBy: AM8P189CA0010.EURP189.PROD.OUTLOOK.COM (2603:10a6:20b:218::15) To DB8PR04MB6523.eurprd04.prod.outlook.com (2603:10a6:10:10f::26) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.80.121] (81.173.50.109) by AM8P189CA0010.EURP189.PROD.OUTLOOK.COM (2603:10a6:20b:218::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3805.16 via Frontend Transport; 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X-OriginatorOrg: topic.nl X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jan 2021 08:45:45.3362 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 36b091a1-68fb-4519-48c9-08d8c3691a6c X-MS-Exchange-CrossTenant-Id: 449607a5-3517-482d-8d16-41dd868cbda3 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=449607a5-3517-482d-8d16-41dd868cbda3;Ip=[40.68.112.65];Helo=[westeu12-emailsignatures-cloud.codetwo.com] X-MS-Exchange-CrossTenant-AuthSource: VE1EUR01FT019.eop-EUR01.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR04MB5604 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Andrew, Response below... Met vriendelijke groet / kind regards,=0A= =0A= Mike Looijmans=0A= System Expert=0A= =0A= =0A= TOPIC Embedded Products B.V.=0A= Materiaalweg 4, 5681 RJ Best=0A= The Netherlands=0A= =0A= T: +31 (0) 499 33 69 69=0A= E: mike.looijmans@topicproducts.com=0A= W: www.topicproducts.com=0A= =0A= Please consider the environment before printing this e-mail=0A= On 28-01-2021 02:56, Andrew Lunn wrote: > On Tue, Jan 26, 2021 at 08:33:37AM +0100, Mike Looijmans wrote: >> The mdio_bus reset code first de-asserted the reset by allocating with >> GPIOD_OUT_LOW, then asserted and de-asserted again. In other words, if >> the reset signal defaulted to asserted, there'd be a short "spike" >> before the reset. >> >> Instead, directly assert the reset signal using GPIOD_OUT_HIGH, this >> removes the spike and also removes a line of code since the signal >> is already high. >=20 > Hi Mike >=20 > Did you look at the per PHY reset? mdiobus_register_gpiod() gets the > GPIO with GPIOD_OUT_LOW. mdiobus_register_device() then immediately > sets it high. >=20 > So it looks like it suffers from the same problem. Well, now that I have your attention... The per PHY reset was more broken, it first probes the MDIO bus to see if t= he=20 PHY is there, and only after that it controls the reset line. So if the res= et=20 defaults to "asserted", the PHY will not work because it didn't respond whe= n=20 the MDIO went looking for it. I haven't quite figured out how this was=20 supposed to work, but at least for the case of one MDIO bus, one PHY=20 configured through devicetree it didn't work as one would expect. I added a= =20 few printk statements to reveal that this was indeed the case. This issue also makes the PHY hardware reset useless - if the PHY is in som= e=20 non-responsive state, the MDIO won't get a response and report the PHY as=20 missing before even attempting to assert/de-assert the reset line. This was with a 5.4 kernel, but as far as I could see this hasn't changed=20 since then. My solution to that was to move to the MDIO bus reset, since that at least= =20 happened before interrogating the devices on the bus. This revealed the iss= ue=20 with the extra "spike" while evaluating that, which is something that I cou= ld=20 easily solve and upstream. Probably these issues were never dicovered because usually there's a pull-u= p=20 of some kind on the (active-low) reset signal of the PHYs. That hides the=20 spike and also hides the fact that the per-phy reset doesn't actually work.= We=20 only discovered the issue when we changed that to a pull-down and suddenly = the=20 phy failed to probe. The way that the MDIO bus is being populated seemed rather complex to me, s= o=20 chances of breaking things are quite high there...