Received-SPF: pass (google.com: domain of linux-kernel+bounces-111966-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:40f1:3f00::1 as permitted sender) client-ip=2604:1380:40f1:3f00::1;
Date: Fri, 22 Mar 2024 19:51:20 +0100
From: Andrew Lunn <andrew@lunn.ch>
To: Ayush Singh <ayushdevel1325@gmail.com>
Cc: open list <linux-kernel@vger.kernel.org>, jkridner@beagleboard.org,
	robertcnelson@beagleboard.org, lorforlinux@beagleboard.org,
	Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>, Nishanth Menon <nm@ti.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Tero Kristo <kristo@kernel.org>,
	Derek Kiernan <derek.kiernan@amd.com>,
	Dragan Cvetic <dragan.cvetic@amd.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Vaishnav M A <vaishnav.a@ti.com>, Mark Brown <broonie@kernel.org>,
	Johan Hovold <johan@kernel.org>, Alex Elder <elder@kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@vger.kernel.org>,
	"moderated list:ARM/TEXAS INSTRUMENTS K3 ARCHITECTURE" <linux-arm-kernel@lists.infradead.org>,
	"open list:SPI SUBSYSTEM" <linux-spi@vger.kernel.org>,
	"moderated list:GREYBUS SUBSYSTEM" <greybus-dev@lists.linaro.org>,
	Vaishnav M A <vaishnav@beagleboard.org>,
	Michael Walle <mwalle@kernel.org>
Subject: Re: [PATCH v4 1/5] dt-bindings: misc: Add mikrobus-connector
Message-ID: <362aace1-2e6a-4b50-acf8-6dccafd44973@lunn.ch>
References: <20240317193714.403132-1-ayushdevel1325@gmail.com>
 <20240317193714.403132-2-ayushdevel1325@gmail.com>
 <711ff5ea-244d-4b64-a39c-3f2da63e30c0@gmail.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <711ff5ea-244d-4b64-a39c-3f2da63e30c0@gmail.com>

> After going through all the discussions here, I have a few questions:
> 
> 1. Is the old `*_register_device(controller, board_info)` style discouraged
> in favor of using device tree, at least for drivers using multiple
> fundamental buses (i2c, spi, etc)?

Historically, they were used in board files, where you needed to write
C code for every single board. That did not scale, which is why we
swapped to DT.

board_info is still useful, e.g. for platforms which don't have DT. I
support a few amd64 boards where i need to use a platform driver to
instantiate some I2C and MDIO devices. But in general DT is much
easier to use.

> 2. Is the preferred way to handle virtual devices (like those created by
> greybus subsystem) now device tree? Is that one of the blockers for greybus
> i2c, spi etc to still be in staging?

I would not say they are virtual. They do exist. They are just not
memory mapped like most devices, but in another address space, one
which you access via RPCs.

> 
> 3. How are virtual devices created in device tree? If I register an i2c
> adapter using `i2c_add_adapter`, is the device tree entry is dynamically
> created, which can then be used by a device tree overlay?

As far as i'm aware, there are no examples today. You are doing
something different, something new. Adding these dynamic devices to DT
is just a suggestion from me, as a good way to solve your problem. You
will need to look into the DT core and figure out how to do it.

     Andrew