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Message-ID: <5cb69afd-044d-deb8-7f81-2f189e4a018b@suse.com> Date: Thu, 27 Apr 2023 09:44:27 +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?Marek_Marczykowski-G=c3=b3recki?= Cc: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , xen-devel@lists.xenproject.org, Andrew Cooper , George Dunlap , Julien Grall , Stefano Stabellini , Wei Liu 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: FR2P281CA0143.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:98::16) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AM7PR04MB7013:EE_ X-MS-Office365-Filtering-Correlation-Id: a9142d45-1d5b-4a47-067b-08db46f33b71 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.) > > I have mirrored the approach used for IO ports, with similar thinking, > and I read the above as you agree. Does it mean this patch is okay, > or you request some change here? Sorry, I've yet to get to look at v2 itself. So far I've only looked at Roger's response. Jan