From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp119.sbc.mail.sp1.yahoo.com (smtp119.sbc.mail.sp1.yahoo.com [69.147.64.92]) by ozlabs.org (Postfix) with SMTP id CE600DDED6 for ; Mon, 30 Jun 2008 14:10:28 +1000 (EST) From: David Brownell To: "Grant Likely" Subject: Re: [PATCH 2/4] spi: split up spi_new_device() to allow two stage registration. Date: Sun, 29 Jun 2008 21:10:25 -0700 References: <20080516193054.28030.35126.stgit@trillian.secretlab.ca> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Message-Id: <200806292110.25793.david-b@pacbell.net> Cc: linuxppc-dev@ozlabs.org, fabrizio.garetto@gmail.com, linux-kernel@vger.kernel.org, spi-devel-general@lists.sourceforge.net List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tuesday 17 June 2008, Grant Likely wrote: > >>> This patch splits the allocation and registration portions of code out > >>> of spi_new_device() and creates three new functions; spi_alloc_device(), > >>> spi_register_device(), and spi_device_release(). > >> > >> I have no problem with the first two, but why the last? > >> > >> If the devices are always allocated by spi_alloc_device() as > >> they should be -- probably through an intermediary -- the > >> only public function necessary for that cleanup should be > >> the existing spi_dev_put(). > > > > Ah, okay.  I'm still a bit fuzzy on the device model conventions. > > I'll remove that then. > > I've dug into this some more.  spi_alloc_device only allocates the > memory.  It doesn't call device_initialize() to initialize the kref. Well, the driver model idiom is initialize() then add(), with register() calls combining the two. An alloc() is just a bit outside those core idioms ... But one alloc() example is platform_device_alloc(), which does the device_initialize() call ... followed by platform_device_add(). The spi_new_device() call does a bunch of stuff beyond a register(), but it also calls device_register(). > All of that behaviour is handled within device_register().  Therefore > if a driver uses spi_alloc_device() and then if a later part of the > initialization fails before spi_register_device() is called, then the > alloc'd memory needs to be freed, but spi_dev_put() won't work because > the kobj isn't set up so I need another function to handle freeing it > in on a failure path. I see ... > Should I switch things around to do device_initialize() in the alloc > function Yes. > and call device_add() instead of device_register() in the > spi_register_device() function? You should also rename it to spi_add_device(), since register() calls always do the initialize() rather than having it done for them in advance. People rely on those names supporting that pattern (as they should). > Is that sufficient to make put_device() work? Looks like it to me. Calling device_initialize() will do a kobject_init(), which is documented as requiring a kobject_put() to clean up ... that's all put_device() will ever do. - Dave