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Wed, 15 Jul 2020 10:32:14 +0200 (CEST) From: Markus Armbruster To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: sysbus_create_simple Vs qdev_create References: Date: Wed, 15 Jul 2020 10:32:14 +0200 In-Reply-To: ("Philippe =?utf-8?Q?Mathieu-Daud=C3=A9=22's?= message of "Tue, 14 Jul 2020 19:02:24 +0200") Message-ID: <87365t18mp.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=armbru@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.81; envelope-from=armbru@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 02:01:40 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Pratik Parvati Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Philippe Mathieu-Daud=C3=A9 writes: > Hi Pratik, > > On 7/14/20 6:17 PM, Pratik Parvati wrote: >> Here is a brief context that might help you. >> I am referring hw/arm/versatilepb.c >>=20 >> The ARM PrimeCell UART (PL011) device created as follows >>=20 >> dev =3D qdev_create(NULL, "pl011"); >> s =3D SYS_BUS_DEVICE(dev); >> qdev_prop_set_chr(dev, "chardev", chr); >> qdev_init_nofail(dev); >> sysbus_mmio_map(s, 0, addr); >> sysbus_connect_irq(s, 0, irq); This is pl011_create(). Since recent merge commit 6675a653d2e, it's dev =3D qdev_new("pl011"); s =3D SYS_BUS_DEVICE(dev); qdev_prop_set_chr(dev, "chardev", chr); sysbus_realize_and_unref(s, &error_fatal); sysbus_mmio_map(s, 0, addr); sysbus_connect_irq(s, 0, irq); >> >> Whereas the PL031 RTC device is created as >>=20 >> /* Add PL031 Real Time Clock. */ >> sysbus_create_simple("pl031", 0x101e8000, pic[10]); >>=20 >> What is the difference between these two devices creation? > > Both devices inherit SysBusDevice, which itself inherits QDev. Yes: TYPE_SYS_BUS_DEVICE is a subtype of TYPE_DEVICE. > You can create QDev objects with the qdev API, and > SysBusDevice objects with the sysbus API. Yes. qdev_new(), qdev_realize_and_unref(), ... work with DeviceState * (the C type of an instance of QOM TYPE_DEVICE). sysbus_realize_and_unref(), ... work with SysBusDevice * (the C type of an instance of QOM TYPE_SYS_BUS_DEVICE). Since TYPE_SYS_BUS_DEVICE is a subtype of TYPE_DEVICE, you can safely use qdev_ functions with sysbus devices. Example: pl011_create() uses qdev_new() to create a sysbus device. That's fine. > sysbus_create_simple() is a condensed helper, but only allow you > to pass qemu_irq objects, not a 'chardev' property. So for this > case you have to use the qdev API instead. Yes. It's a helper that combines creating a sysbus device, wiring up one MMIO region and one IRQ, and realizing. If you need to configure or wire up more than that, you can't use it. >> How do I know >> which method to use while creating an object? > > SysBusDevice are plugged onto a bus. QDev aren't. > The sysbus API results in smaller code, easier to review. The general pattern for a stand-alone device is dev =3D qdev_new(type_name); set properties and wire up stuff... qdev_realize_and_unref(dev, bus, &err); When this is to be done in device code, say to create a component device, the split between .instance_init() and .realize() complicates things. If interested, ask and I'll explain. There are quite a few wrappers around qdev_ functions for various subtypes of TYPE_DEVICE. Use them to make your code more concise and easier to understand. Example: sysbus_realize_and_unref(). There are also convenience functions that capture special cases of the entire general pattern. Example: sysbus_create_simple(). Hope this helps!