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Wysocki" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/2] regmap: teach regmap to use raw spinlocks if requested in the config Thread-Topic: [PATCH 1/2] regmap: teach regmap to use raw spinlocks if requested in the config Thread-Index: AQHXmfLp4ns/CR9SwkOJBzcXz4/yJ6uGaLyAgAEgBoA= Date: Fri, 27 Aug 2021 16:12:28 +0000 Message-ID: <20210827161227.4pnaglgctikobpf6@skbuf> References: <20210825205041.927788-1-vladimir.oltean@nxp.com> <20210825205041.927788-2-vladimir.oltean@nxp.com> <875yvr3j5c.ffs@tglx> In-Reply-To: <875yvr3j5c.ffs@tglx> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: linutronix.de; dkim=none (message not signed) header.d=none;linutronix.de; dmarc=none action=none header.from=nxp.com; x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 279d4c55-b0d8-4db0-0353-08d96975773f x-ms-traffictypediagnostic: VE1PR04MB6512: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:7691; 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charset="us-ascii" Content-ID: <41320510ACF9E04C9E2AE7CBCE43A353@eurprd04.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB5136.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 279d4c55-b0d8-4db0-0353-08d96975773f X-MS-Exchange-CrossTenant-originalarrivaltime: 27 Aug 2021 16:12:28.1025 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: TpRdVcnwg64P6bVXMdtPYeeE0mxV2CTtpAXhjjEMxyU0xHLAe4qsWTAiSZdIcertQNaaKv1DGM+AyW1RoEc//g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VE1PR04MB6512 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 27, 2021 at 01:01:35AM +0200, Thomas Gleixner wrote: > On Wed, Aug 25 2021 at 23:50, Vladimir Oltean wrote: > > It seems reasonable for regmap to have an option use a raw spinlock too= , > > so add that in the config such that drivers can request it. > > What's reasonable about that? > > What exactly prevents the regmap locking to use a raw spinlock > unconditionally? > > Even for the case where the regmap is not dealing with irq chips it does > not make any sense to protect low level operations on shared register > with a regular spinlock. I might be missing something though... Mark, any comments? Generally it is said that misusing raw spinlocks has detrimential performance upon the real-time aspects of the system, and I don't really have a good feeling for what constitutes misuse vs what is truly justified (in fact I did start the thread with "apologies for my novice level of understanding"). On the other hand, while it does seem a bit too much overhead for sequences of MMIO reads/writes to be able to be preempted, it doesn't sound like it would break something either, so... But I will say that I've tested that and it would solve both my problems (the stack trace with ls-extirq and the fact that I would like to avoid reworking the ls-extirq driver too much), as well as problems I never knew I had: it turns out, armada_37xx_irq_set_type() uses regmap too (and a sleepable spin lock too - irq_lock). The latter would still have to be manually patched out.=