Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Peng Fan <peng.fan@nxp.com>
To:     Ahmad Fatoum <a.fatoum@pengutronix.de>,
        Abel Vesa <abelvesa@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        dl-linux-imx <linux-imx@nxp.com>
CC:     "Peng Fan (OSS)" <peng.fan@oss.nxp.com>,
        "linux-clk@vger.kernel.org" <linux-clk@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2] clk: imx: composite-8m: fix clock pauses when set_rate
 would be a no-op
Thread-Topic: [PATCH v2] clk: imx: composite-8m: fix clock pauses when
 set_rate would be a no-op
Thread-Index: AQHZyQhHU4zMCTsVi0qS8SrTg71ajK/efu0w
Date:   Mon, 7 Aug 2023 08:24:49 +0000
Message-ID: <DU0PR04MB941738BCFEB341B4DADA49AD880CA@DU0PR04MB9417.eurprd04.prod.outlook.com>
References: <20230807082201.2332746-1-a.fatoum@pengutronix.de>
In-Reply-To: <20230807082201.2332746-1-a.fatoum@pengutronix.de>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?P++CUpf+yWQ7jDgVsa+tzB/znwUODnIliNPHe85H0d/MTiXqEDg0fuVLg6Bk?=
 =?us-ascii?Q?g8IJXuN1HZiO0+xW+eAah6SB9FnY8TFcBgFTi0Zletn+a+cIaQyXlzBZhhea?=
 =?us-ascii?Q?slMBvQU4SbN7tK6I+c7+ZTZdmBkkdlIzegabC9K4UBtnx4IsdZ1SC1fhvW+t?=
 =?us-ascii?Q?eF9iWcCxrwsOTMevCVxod56nyFxcaSPYhHs302wZ3jMFzsRBnWIlEnxFhvDH?=
 =?us-ascii?Q?nIU7GfEqdRWZg0znw4KJtKnAQlMZRccuekfaDhyokQRXi2ZjvrdCXbFeca5Z?=
 =?us-ascii?Q?NS9sErrv7LJ8heErSDB/MDDjOeSRcFBaJt8NGyV3RgPYzKaJ68WEXDesIk3z?=
 =?us-ascii?Q?NJm5qaeFfNTc4nFqiZNtHvOYUxODjWoMmCXZFS3HB2r5Eu6a35FJ8f3lUaXh?=
 =?us-ascii?Q?tK2H8alTy/qd3JXk3AXZw5oj7JICJ6GSJ7anztX5Dq2YQCwOc6QCWaKs9cuF?=
 =?us-ascii?Q?3u3nng2I3T2x4r87Y1Vfuu2RkNP2R3B87UYxHJ0RTeX4mBL5rJPndladoN4k?=
 =?us-ascii?Q?NmxIkSoR+QAxiVtZ3RS28RnKSiGyslnQDUX/+T+zdzk0O1MsaRy4NJewmHid?=
 =?us-ascii?Q?7VlF7yQhsEvCsl5pn//tSd1sQP4vLtYbkigzf/FcUgaF/eEUBPnmFBcM3PAC?=
 =?us-ascii?Q?sEDE0MbjmUn8aVqyIf1pNpAnDY6vP6ndhtK0DV2TKmsBpaJgS0zcnMLVxtc9?=
 =?us-ascii?Q?65i8tCqFNEFgWLw2+TGQTmhBJncag18tqblPwivegkobrSz5YXaujtuPG9mr?=
 =?us-ascii?Q?fIVdiQFFZGfswh3wCCBigXDarxTz264CedOMJN/nEGlj7mjYcHOtBzSI6hUF?=
 =?us-ascii?Q?qLK8IBGZDUVcGLF4cZjtGUBUwpJrBA922acrPWGEbNq7CpxKtYRXG8/pO91i?=
 =?us-ascii?Q?EhqutF6SyS7mON0MmzMyFtNP3foR/4sEqeppSlQ7xh0Sn/rgnEWugT19Y3ZD?=
 =?us-ascii?Q?KL6UdmTb4cJtGNUBI5e1AjQbwjzk1mauBuF2p3jnShXKPaiDGEiFkhkMA/6r?=
 =?us-ascii?Q?iTWVBhmHzU2xtNuKpfeeSvQITM/CUbxi1YTf9nfc+DYkqBUIKgFvl1qdptVI?=
 =?us-ascii?Q?0q1JYxwEhx9r6rNHwo3Uq1wtkG7pbVD4Sf8zyydWKj08AVxY54SB+k4Uf5bt?=
 =?us-ascii?Q?Aa263kPZiZypLD5ZhB588LViR0nLRPlFVH101qXXTAeRId/YkWvyk1KURqAh?=
 =?us-ascii?Q?4p42V5vmEK4I7n2efGOsDnUnIqMosOq5Xc7/0+ZdyttHoh74NPG3HfWpTK3i?=
 =?us-ascii?Q?/AC8im/5OmrE6VJ6OmmtIuYyChGvjcYcz2gWXw+/O8wDh0g/kmWhmMLYj78e?=
 =?us-ascii?Q?NoQ+Tk+J9Uml7z/mcMlT/9hoWtRR20dv4G9lVv+KGpYLhJ/KoaJ2yx0NcJ07?=
 =?us-ascii?Q?MB+thSqgsWzBTCAe72mq2OMiRlTj+mRsTI69OfaFu9cz8MOoGd7sHB1LY1nG?=
 =?us-ascii?Q?C1oSlEMpMaTWDvSLW7hUIKFkLZ+9P+ff4tQACFccqYpiRH+Uoii0MtubmEtZ?=
 =?us-ascii?Q?ls5QU/t95p40+Ykuf3mWjxhQk4OPcu9EYSGLWgCZuIQ4fsJZxHHyZqWUfj4N?=
 =?us-ascii?Q?R46CVJBNIY+7/o9SJf4=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-OriginatorOrg: nxp.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: DU0PR04MB9417.eurprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 81d58c51-388d-4253-9eb5-08db971fc46d
X-MS-Exchange-CrossTenant-originalarrivaltime: 07 Aug 2023 08:24:49.8026
 (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: tpO/YW/0RheahC+IqqMQoq1dDdKYgBzQBQNsTz4nHYTa990RxFVejWN/v520ikbbMOGjWvhkjC8qbn3oKXvYcg==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAXPR04MB8541
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED,
        RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> Subject: [PATCH v2] clk: imx: composite-8m: fix clock pauses when set_rat=
e
> would be a no-op
>=20
> Reconfiguring the clock divider to the exact same value is observed on an
> i.MX8MN to often cause a longer than usual clock pause, probably because
> the divider restarts counting whenever the register is rewritten.
>=20
> This issue doesn't show up normally, because the clock framework will tak=
e
> care to not call set_rate when the clock rate is the same.
> However, when we reconfigure an upstream clock, the common code will
> call set_rate with the newly calculated rate on all children, e.g.:
>=20
>   - sai5 is running normally and divides Audio PLL out by 16.
>   - Audio PLL rate is increased by 32Hz (glitch-free kdiv change)
>   - rates for children are recalculated and rates are set recursively
>   - imx8m_clk_composite_divider_set_rate(sai5) is called with
>     32/16 =3D 2Hz more
>   - imx8m_clk_composite_divider_set_rate computes same divider as before
>   - divider register is written, so it restarts counting from zero and
>     MCLK is briefly paused, so instead of e.g. 40ns, MCLK is low for 120n=
s.
>=20
> Some external clock consumers can be upset by such unexpected clock
> pauses, so let's make sure we only rewrite the divider value when the val=
ue
> to be written is actually different.
>=20
> Fixes: d3ff9728134e ("clk: imx: Add imx composite clock")
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Reviewed-by: Peng Fan <peng.fan@nxp.com>

Regards,
Peng.