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Miller" Subject: Re: [PATCH 1/4] dt-bindings: net: dsa: nxp,sja1105: Add reset-gpios property Message-ID: <20250910153454.ibh6w7ntxraqvftb@skbuf> References: <20250910-imx8mp-prt8ml-v1-0-fd04aed15670@pengutronix.de> <20250910-imx8mp-prt8ml-v1-1-fd04aed15670@pengutronix.de> <20250910125611.wmyw2b4jjtxlhsqw@skbuf> <20250910143044.jfq5fsv2rlsrr5ku@pengutronix.de> <20250910144328.do6t5ilfeclm2xa4@skbuf> <693c3d1e-a65b-47ea-9b21-ce1d4a772066@sirena.org.uk> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <693c3d1e-a65b-47ea-9b21-ce1d4a772066@sirena.org.uk> X-ClientProxiedBy: VI1P195CA0094.EURP195.PROD.OUTLOOK.COM (2603:10a6:802:59::47) To AM8PR04MB7779.eurprd04.prod.outlook.com (2603:10a6:20b:24b::14) Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AM8PR04MB7779:EE_|AM9PR04MB8507:EE_ X-MS-Office365-Filtering-Correlation-Id: 2cc87ba1-2fdc-4aab-bc0b-08ddf07f9a7a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|1800799024|376014|7416014|366016|19092799006; 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I suspect > that what it's trying to say is that the reset signal only works with > stable power and clocks, that it must be held low for the 5us while > those conditions hold and that you have to do at least one cold reset > after power on. The above wording is pretty common in datasheets and I > know in a bunch of cases it was carried forward kind of blindly rather > than looking at the actual device requirements. No, it doesn't say that, and I had discussions with the application engineering team for this chip about this :-/ I can't comment on anything extrapolated outside of the SJA1105/SJA1110. > > It really depends on a lot of factors including the reset timing and > > supply voltage distribution of the PCB, but RST_N has essentially 2 > > purposes. One is ensuring proper POR sequencing, the other is cold > > resetting at runtime. You can do the latter over SPI with identical > > outcome, which leaves proper POR sequencing, which is not best served by > > a GPIO in my experience. > > I'm not sure not including the signal in the DT bindings is going to > influence board designers much either way TBH. Either way, something has to nudge at least the software developer towards finding and reading the vendor's relevant documentation. In that sense, 'reset-gpios' is misleading to say the least, because everyone sees a reset GPIO and has the human tendency to think there isn't anything more to be known about it (like I also did). To be clear, I'm saying that supporting 'reset-gpios' in this driver was a mistake, at least in the form where its supplies and clocks aren't also under control. I'm not sure it's a mistake that we need to document, and if we do, there need to be a lot more disclaimers. Also, I'm pretty sure nothing will break if driver support for it is simply removed.