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Message-ID: Date: Wed, 26 Apr 2023 10:24:28 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v2] ns16550: enable memory decoding on MMIO-based PCI console card Content-Language: en-US To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: xen-devel@lists.xenproject.org, Andrew Cooper , George Dunlap , Julien Grall , Stefano Stabellini , Wei Liu , =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= References: <20230425143902.142571-1-marmarek@invisiblethingslab.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR2P281CA0174.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:9f::11) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AM9PR04MB7601:EE_ X-MS-Office365-Filtering-Correlation-Id: 619b9401-3af9-4ed3-52c6-08db462fa7ef X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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> > Don't you want to read the current command register first and just > or PCI_COMMAND_MEMORY? > > I see that for IO decoding we already do it this way, but I'm not sure > whether it could cause issues down the road by unintentionally > disabling command flags. Quite some time ago I asked myself the same question when seeing that code, but I concluded that perhaps none of the bits are really sensible to be set for a device as simple as a serial one. I'm actually thinking that for such a device to be used during early boot, it might even be helpful if bits like PARITY or SERR get cleared. (Of course if any of that was really the intention of the change introducing that code, it should have come with a code comment.) Jan