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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 DBBPR04MB7708.eurprd04.prod.outlook.com (2603:10a6:10:20d::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3805.17; Tue, 2 Feb 2021 11:40:14 +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 15.20.3805.024; Tue, 2 Feb 2021 11:40:14 +0000 Subject: Re: [PATCH] net: mdiobus: Prevent spike on MDIO bus reset signal To: Andrew Lunn , Russell King - ARM Linux admin CC: netdev@vger.kernel.org, "David S. Miller" , Heiner Kallweit , Jakub Kicinski , linux-kernel@vger.kernel.org References: <20210126073337.20393-1-mike.looijmans@topic.nl> <20210126134937.GI1551@shell.armlinux.org.uk> <20210128002555.GQ1551@shell.armlinux.org.uk> <1b153bce-a66a-45ee-a5c6-963ea6fb1c82.949ef384-8293-46b8-903f-40a477c056ae.47109184-a5be-4b1d-bb22-724baf83e536@emailsignatures365.codetwo.com> <1b153bce-a66a-45ee-a5c6-963ea6fb1c82.0d2bd5fa-15cc-4b27-b94e-83614f9e5b38.a2a17a1f-7cb0-46c3-bdd8-65266e08a153@emailsignatures365.codetwo.com> From: Mike Looijmans Organization: Topic Message-ID: <7cbe00ba-d762-7e18-6936-ae8cbd493ade@topic.nl> Date: Tue, 2 Feb 2021 12:40:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Content-Language: en-US X-Originating-IP: [83.128.90.119] X-ClientProxiedBy: AM9P191CA0019.EURP191.PROD.OUTLOOK.COM (2603:10a6:20b:21c::24) To DB8PR04MB6523.eurprd04.prod.outlook.com (2603:10a6:10:10f::26) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.130] (83.128.90.119) by AM9P191CA0019.EURP191.PROD.OUTLOOK.COM (2603:10a6:20b:21c::24) 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: 02 Feb 2021 11:40:22.0246 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 95356cf6-7f7d-45c8-1745-08d8c76f532b 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: DB5EUR01FT019.eop-EUR01.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB8PR04MB6905 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 02:12, Andrew Lunn wrote: > On Thu, Jan 28, 2021 at 12:25:55AM +0000, Russell King - ARM Linux admin = wrote: >> On Thu, Jan 28, 2021 at 01:00:57AM +0100, Andrew Lunn wrote: >>> On Tue, Jan 26, 2021 at 01:49:38PM +0000, Russell King - ARM Linux admi= n wrote: >>>> On Tue, Jan 26, 2021 at 02:14:40PM +0100, 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 wi= th >>>>>> 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. >>>>> Hi Mike >>>>> >>>>> This however appears to remove the reset pulse, if the reset line was >>>>> already low to start with. Notice you left >>>>> >>>>> fsleep(bus->reset_delay_us); >>>>> >>>>> without any action before it? What are we now waiting for? Most data >>>>> sheets talk of a reset pulse. Take the reset line high, wait for some >>>>> time, take the reset low, wait for some time, and then start talking >>>>> to the PHY. I think with this patch, we have lost the guarantee of a >>>>> low to high transition. >>>>> >>>>> Is this spike, followed by a pulse actually causing you problems? If >>>>> so, i would actually suggest adding another delay, to stretch the >>>>> spike. We have no control over the initial state of the reset line, i= t >>>>> is how the bootloader left it, we have to handle both states. >>>> Andrew, I don't get what you're saying. >>>> >>>> Here is what happens depending on the pre-existing state of the >>>> reset signal: >>>> >>>> Reset (previously asserted): ~~~|_|~~~~|_______ >>>> Reset (previously deasserted): _____|~~~~|_______ >>>> ^ ^ ^ >>>> A B C >>>> >>>> At point A, the low going transition is because the reset line is >>>> requested using GPIOD_OUT_LOW. If the line is successfully requested, >>>> the first thing we do is set it high _without_ any delay. This is >>>> point B. So, a glitch occurs between A and B. >>>> >>>> We then fsleep() and finally set the GPIO low at point C. >>>> >>>> Requesting the line using GPIOD_OUT_HIGH eliminates the A and B >>>> transitions. Instead we get: >>>> >>>> Reset (previously asserted) : ~~~~~~~~~~|______ >>>> Reset (previously deasserted): ____|~~~~~|______ >>>> ^ ^ >>>> A C >>>> >>>> Where A and C are the points described above in the code. Point B >>>> has been eliminated. >>>> >>>> Therefore, to me the patch looks entirely reasonable and correct. >>> I wonder if there are any PHYs which actually need a pulse? Would it >>> be better to have: >>> >>> Reset (previously asserted): ~~~|____|~~~~|_______ >>> Reset (previously deasserted): ________|~~~~|_______ >>> ^ ^ ^ ^ >>> A B C D >>> >>> Point D is where we actually start talking to the PHY. C-D is >>> reset-post-delay-us, and defaults to 0, but can be set via DT. B-C is >>> reset-delay-us, and defaults to 10us, but can be set via DT. >>> Currently A-B is '0', so we get the glitch. But should we make A-B the >>> same as B-C, so we get a real pulse? >> I do not see any need for A-B - what is the reason for it? > If level is all that matters, then it is not needed. If a PHY needs an > actual pulse, both a raising and a falling edge, we potentially don't > get the rising edge now. We only caught the "spike" because the reset GPIO was controlled by a=20 GPIO expander, so it took about a millisecond to toggle it. With a=20 "local" GPIO controller, the pulse duration would be below the=20 microsecond range and most PHYs would never see it. > But the datasheets you have looked at all seem to talk about level, > not pulse. So lets go with this. > > Reviewed-by: Andrew Lunn > > Andrew Just wondering, now, a v2 patch isn't needed? Or should I amend the=20 commit text? --=20 Mike Looijmans