Date:   Sat, 11 Feb 2023 23:36:43 +0200
From:   Vladimir Oltean <vladimir.oltean@nxp.com>
To:     Andrew Lunn <andrew@lunn.ch>
Cc:     Saravana Kannan <saravanak@google.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Lee Jones <lee@kernel.org>,
        Colin Foster <colin.foster@in-advantage.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org
Subject: Re: Advice on MFD-style probing of DSA switch SoCs
Message-ID: <20230211213643.talp76wceyc7mypp@skbuf>
References: <20221222134844.lbzyx5hz7z5n763n@skbuf>
 <4263dc33-0344-16b6-df22-1db9718721b1@linaro.org>
 <20221223134459.6bmiidn4mp6mnggx@skbuf>
 <CAGETcx8De_qm9hVtK5CznfWke9nmOfV8OcvAW6kmwyeb7APr=g@mail.gmail.com>
 <20230211012755.wh4unmkzibdyo4ln@skbuf>
 <Y+e5TzNRckDADd5d@lunn.ch>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y+e5TzNRckDADd5d@lunn.ch>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?MF8IICk+w5UCp7xYAGV/pWYMN+ZAD+Px0AjlxOEFYNdk5IAiXQvepO4VoWvT?=
 =?us-ascii?Q?MKTVvcBhGVEVUy4beUcY6ADvPqwQIqFP4M4vJm13r7M5f5fx9IMuOsFDkfxZ?=
 =?us-ascii?Q?Ewi4zfe+NmN9QpXpL4rPDpXgHS3Jh9WtdX7Kd/BrKOa+UFYXIFveFdQxsrfe?=
 =?us-ascii?Q?W3n7kmXSNaxF4fKnGWVA9H1UUPeHGhlo2fpJqvoh2A4VXWfHYE/3V2DrLzbJ?=
 =?us-ascii?Q?GJv9/7LEe57Lvb4Ntiw2ffdcEBLnjVXJeAcJHYxIXnDPG8gFPc9hj9jdBPt5?=
 =?us-ascii?Q?20FbNsW3kTzIw41+gZSOkILW8t7tbp3tuWt1s4xtWJfeC74eTPIlSThNyjK5?=
 =?us-ascii?Q?DGkfdRry4apz1oygHz8hA0vK7Be7o50P6ORjRYvKTlels+oZD5gq7zNGSJa9?=
 =?us-ascii?Q?i+pmu6dOhJwESNtohdC/b4gWDGnTOumSyxw56iPZtwzAoY1rSyb9NMWyqbQC?=
 =?us-ascii?Q?rzF2POZ6jlGTZShUVbh7YeAK9u9CRpee+YBkEukXjJiqXJhuJjV34aRT1SjQ?=
 =?us-ascii?Q?jNrTn3VIdndzn7z69QYeslw3OjEzpJVZHdu6Qcgig1eb4k7aSQseWnLdvlTu?=
 =?us-ascii?Q?/PH7KoA1WsldRSXDeovkZ9Lroy/hdjDMTa8AuvzJ9w/PjploJjlD+Elx/8sQ?=
 =?us-ascii?Q?BLoQP1bzZ5O1kGDkZpti41cXEq+Xup1oH11LL51zoBLVb5bhCU3qyavjGlZG?=
 =?us-ascii?Q?rvLnmu3JxkQ0Bo5uSsnfMLfoHxDZKCRMdMRgW9eIlec4vOfTnCTwwW1CVsip?=
 =?us-ascii?Q?zT9KntNIppZIUABWvb/2SX9mIJkyL+tBTvrnV9p7EZEBQf1/cDxOXDqe9MkY?=
 =?us-ascii?Q?401fKl9kzmOt4IggHVd0gTeJ/Yf2I/utC5obdtUx3erw4rzhkOheKPlh12o5?=
 =?us-ascii?Q?8r1uHevCZlc8tZwAsTt8ZwfaMc04DfC97SMY7UbyjK2kJZw+cIfsXzcX3OLB?=
 =?us-ascii?Q?glBLkNdIGMhTijW1idOvdl2nGAZEnVefZY2N7Zwt33TdZm7zFMD9ZbOA16Aj?=
 =?us-ascii?Q?Ebhc9kh5DOU2Q3thgyXoR21QBusWfAbYo60y01kDoiY6DgViSIQVd6jfHUdb?=
 =?us-ascii?Q?EYgZjoJmvqueLNsVlpsLCg8lQ46QrTI9x+hypcoUBBjjYsG/j2sFFbI5M08u?=
 =?us-ascii?Q?PcaZTnHJ3b4ZwzFOzOFp+MQCR4KSjT+mI5Dync5lqmA5ekmNNl0LPSmLGf09?=
 =?us-ascii?Q?qTAW+zQoX1hezs6trUrA3zf8j+yAgmbjCB2bNDjam74EPYV5bzBqTpZ1IgZg?=
 =?us-ascii?Q?9RHAFkTrhbIH0F4C7KYbnkyQV1C9y4pkEiW7ShZ217Elo4dGcAqDso/FNJYy?=
 =?us-ascii?Q?EY9axK7m6+0eL6spy4yEz3+LZYC7vAsK4+DLjz1wPb06o+OfsC0AEemZ7Ph2?=
 =?us-ascii?Q?dvTYTXghO2e/ZdLaJzxLo4mNqCoE/+wC1enMP1g2dptdraBI4yeh7tQv1XL+?=
 =?us-ascii?Q?NoLvQa9Zqg0pVFVq5RDxFRGfzCM8AV5wDZtaezvKPIb6AVJ4kDBfQQFslvWq?=
 =?us-ascii?Q?9WB1Ml2PQryQXkPpAZjD3mqRjlN3LjstT+TotEXxMxHU1coSPBIs/9wmFWXo?=
 =?us-ascii?Q?VDPkXF6UygkCNQ5EvdLmDHnOfTnEq980OZdgPRMpU6APU+iqqJCB3wfOlYpV?=
 =?us-ascii?Q?jA=3D=3D?=
X-OriginatorOrg: nxp.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 2f32f789-901b-4720-c452-08db0c781424
X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB5136.eurprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Feb 2023 21:36:47.9275
 (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: JF+PtB0/idv3ik21lSx6Pj6I8FJpxQF+vR/XCzOzm4FTbJvOJ7ZEfpiWMcosnfHx2FPaU6ozDrXA2aHk0AQ46w==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS4PR04MB9507
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Sat, Feb 11, 2023 at 04:50:39PM +0100, Andrew Lunn wrote:
> I'm not sure that is true. The switches probe method should register
> with the driver core any resources a switch provides. So switch #1
> MDIO bus driver is registered during its probe, allowing the probe of
> switch #2 to happen. When switch #2 probes, it should register its
> clock with the common clock framework, etc.
> 
> However, the linking of resources together, the PTP clock in your
> example, should happen in the switches setup() call, which only
> happens once all the switches in the cluster have probed, so all the
> needed resources should be available.
> 
> Because we have these two phases, i think the above setup would work.

I was thinking it wouldn't work because the PTP timer sub-driver would
first have to request the clock input from the CCF, before registering
its own clock output with the CCF. So the driver writer would be forced
to request a clock from the CCF in the probe() phase, if it wanted to
also register as a clock provider in the probe() phase.

I.o.w., switch #1 would get an -EPROBE_DEFER waiting for the clock from
switch #2, before it would get to call dsa_register_switch().

TLDR: the rule "provide all you have in stage 1, request all you need
in stage 2" would only work if you don't need anything to register your
providers.