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Rozycki" CC: "linux-mips@vger.kernel.org" , Paul Burton Subject: Re: [PATCH 1/4] MIPS: cmdline: Remove CONFIG_MIPS_CMDLINE_BUILTIN_EXTEND Thread-Topic: [PATCH 1/4] MIPS: cmdline: Remove CONFIG_MIPS_CMDLINE_BUILTIN_EXTEND Thread-Index: AQHVftk5/yfDqr7FH0WLV65y3YAPuw== Date: Wed, 9 Oct 2019 19:39:11 +0000 Message-ID: <20191009193909.nft6snedx6vb4qpm@pburton-laptop> References: <20191007221951.1889661-1-paul.burton@mips.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: BYAPR01CA0057.prod.exchangelabs.com (2603:10b6:a03:94::34) To MWHPR2201MB1277.namprd22.prod.outlook.com (2603:10b6:301:18::12) user-agent: NeoMutt/20180716 authentication-results: spf=none (sender IP is ) smtp.mailfrom=pburton@wavecomp.com; x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [12.94.197.246] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: e48920bd-d03b-4a03-6804-08d74cf05bb1 x-ms-traffictypediagnostic: MWHPR2201MB1358: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; x-forefront-prvs: 018577E36E x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(7916004)(396003)(376002)(39840400004)(346002)(366004)(136003)(199004)(189003)(316002)(14454004)(478600001)(186003)(25786009)(14444005)(6916009)(256004)(8676002)(81166006)(305945005)(81156014)(7736002)(58126008)(6486002)(9686003)(229853002)(6512007)(8936002)(99286004)(26005)(52116002)(76176011)(3846002)(6116002)(6436002)(6506007)(446003)(11346002)(33716001)(5660300002)(6246003)(66066001)(42882007)(71190400001)(71200400001)(107886003)(44832011)(66446008)(64756008)(66556008)(66476007)(476003)(4326008)(1076003)(486006)(386003)(66946007)(102836004)(2906002)(54906003);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR2201MB1358;H:MWHPR2201MB1277.namprd22.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; received-spf: None (protection.outlook.com: wavecomp.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: DlBBk8xEeFSXizv9zl+c4f5ZwcYIZFMqjdohssOlIhFdySThBt/+/5L6Go2+PHpwfBnbio2njYVk5McqVv0KyQBwAruY4HKdh9M9A0wIYAUgpGgwbUzt+lqvcfX2uKGDTi9jaACSPb2Bii8WTCnuvo8mkasAnOw5oy5RY695MWW3AnhUK70/8TgR6XPuBbzvfgdlzbosb1ylJUJt5n8OwFEP8hSTT14QGDmYl9BrKs8N5MHA2JASkHqaEuh5/Z2WZKVmUVhgnIlL9AhSHmHQxeDEGLLATtZE3RhjnvG3v2oAfq1Pp1DARiIc64cdYMia4neAUUxR+X4/MWgXpr373ZJ3xX7F/AYr7xTbbFsKzqPIm2OY0CenhS47MdHFhyaZzqvY3ZwqvhwlZNezDZcmaRptmgnAouTAvoGpI4t5kn8= Content-Type: text/plain; charset="us-ascii" Content-ID: <26736BF57033B34088F164AB58C05F8E@namprd22.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: mips.com X-MS-Exchange-CrossTenant-Network-Message-Id: e48920bd-d03b-4a03-6804-08d74cf05bb1 X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Oct 2019 19:39:11.4967 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 463607d3-1db3-40a0-8a29-970c56230104 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 3zPJWnAZFm5Q6ZhOTYZH/G5Lclv1B+cQYjXxgs/znrjFy7FvGH1m9dVQXi9ohtNj785zDLbWhpS/RyNSg3QZBQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR2201MB1358 Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Hi Maciej, On Wed, Oct 09, 2019 at 03:13:09PM +0100, Maciej W. Rozycki wrote: > On Wed, 9 Oct 2019, Maciej W. Rozycki wrote: >=20 > > > CONFIG_MIPS_CMDLINE_BUILTIN_EXTEND is not selected by any of our > > > defconfigs, so remove it to simplify the messy command line logic in > > > arch_mem_init() a little. > >=20 > > That sounds like a poor argument for a functional regression to me. I= =20 > > have the option enabled in several configs I have been using just to be= =20 > > able to temporarily override any built-in parameters with ones typed fr= om=20 > > the console monitor's prompt. Is it my mistake that I haven't put it i= n a=20 > > defconfig? For a "functional regression" sure. For removal of an unused code path I'd say not, and presence in defconfigs is generally a reasonable indication of use. The knowledge that you do actually use this is useful information. I'll note that I dislike the idea of overriding options built into the kernel from the bootloader because: 1) Some options just don't work that way & specifying them twice has unexpected effects, so this option gives users another way to screw up. But sure, a user will always be able to screw up if they try hard enough etc etc. 2) As you say yourself a defconfig generally won't (or at least shouldn't) have much of anything in CONFIG_CMDLINE anyway. That means this use case requires someone to build their own kernel whilst explicitly specifying built-in arguments they don't actually want, which I'd consider somewhat niche. Having said that if you find it useful I'm not against keeping that ability, but I think we should do it a little differently by noting that the option is essentially the same as MIPS_CMDLINE_FROM_BOOTLOADER apart from the order in which bootloader & built-in arguments are concatenated. So I'd prefer that we handle this by either providing an option to specify whether CONFIG_CMDLINE is prepended or appended to the bootloader/DTB arguments, or perhaps by adding a separate CONFIG_CMDLINE_PREPEND string. Either one of these should still allow for your use case whilst also allowing the code that has to deal with it to be less of an eyesore. > Elaborating, there's IMO little sense to set MIPS_CMDLINE_BUILTIN_EXTEND= =20 > in a defconfig, because there's usually no default command line to set=20 > there in the first place, as this will be installation-specific. Ergo I= =20 > highly doubt the absence of the setting across the board is due to nobody= =20 > (except for myself) using it. >=20 > Therefore: >=20 > Nacked-by: Maciej W. Rozycki >=20 > NB DECstation systems use a DS1287 or a similar RTC/NVRAM chip to hold=20 > configuration and space is limited there. Up to 37 of kernel command lin= e=20 > characters can be permanently stored, fewer on some systems, and used for= =20 > automatic boot. Conversely when typed at the console monitor prompt ther= e=20 > is no (known to me) limitation as to the length of the kernel command lin= e=20 > requested. >=20 > Therefore a kernel configured for those systems will normally have=20 > several parameters embedded within itself while letting the non-volatile= =20 > storage or user input extend and/or selectively override them, e.g. for a= =20 > different root device or whatever. That's a pretty awful limit. My intent isn't to actively break these 30 year old machines, but the cruft that has built up to deal with their limitations over the years certainly needs some cleanup if it is to remain. Said limitations ought to be documented within the code so that developers have a chance of seeing why options like this exist - otherwise every bit of progress will result in pushback from people using these ancient machines, and I won't allow these antiques to be an anchor tied to the ankles of developers making forward progress on machines that actually have users. There are almost certainly some unmaintained ones whose time is well past up. Thanks, Paul