From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Bird Date: Thu, 13 May 2004 22:46:12 +0000 Subject: Re: Hotplug events for system suspend/resume Message-Id: <40A3FAB4.7090401@am.sony.com> List-Id: References: <20040511010015.GA21831@dhcp193.mvista.com> <20040511230001.GA26569@kroah.com> <40A17251.2000500@mvista.com> <20040512150818.GE10924@kroah.com> In-Reply-To: <20040512150818.GE10924@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Greg KH Cc: Todd Poynor , mochel@digitalimplant.org, linux-hotplug-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Greg KH wrote: > On Tue, May 11, 2004 at 05:39:45PM -0700, Todd Poynor wrote: > >>But again, I'll let the embedded system designers jump in here if they'd >>like to add some insight. In both of the above cases, some ad-hoc >>method of kernel-to-userspace notification could be used, but I am >>trying to gauge interest in using hotplug as a generic notifier for these. > > Ok, I'm not going to accept this until some people who would actually > use it step up and want to push for its inclusion. None of this "patch > by proxy" stuff... Sony is one of MontaVista's customers that is keenly interested in user-space notifiers for power management state changes. We are interested in uniform handling of power-change events, in user space, whether they are initiated by other user apps or from kernel. Here's one use case: The system clock usually runs at 30MHz but it needs to run at at 33MHz when I/O is performed on a particular compact flash controller (but only when I/O is active). Here are the state transitions: 0. System Clock is running at 30MHz 1. Compact Flash card is inserted 2. CF controller is activated and detects CF I/O type 3. kernel notifies that CF I/O is now activated, to user-space PM policy manager 4. User-space PM policy manager changes the clock speed to 33 MHz Here is another case, which is similar, but triggered by application action: 0. System Clock is running at 30MHz and the I/O mentioned above is turned off 1. An application opens up I/O on the compact flash device 2. device driver turns on the I/O, but cannot get operational state. 3. kernel notifies that the CF I/O is now activated, to user-space PM policy manager 4. user-space PM policy manager changes clock speed to 33MHz Pardon the delay in responding, but these things take time to translate, distill and pass on, in international organizations. (And I'm still not sure I got the details right here, please bear with me.) Sony has experience with notifiers using /proc in a 2.4 kernel, so I don't know if we can directly comment on the details of a hotplug-based notification scheme. But I can say that kernel-to-user notifications is an important feature for us. I hope this is helpful. ==============Tim Bird Architecture Group Co-Chair CE Linux Forum Senior Staff Engineer Sony Electronics E-mail: Tim.Bird@am.sony.com ============== ------------------------------------------------------- This SF.Net email is sponsored by: SourceForge.net Broadband Sign-up now for SourceForge Broadband and get the fastest 6.0/768 connection for only $19.95/mo for the first 3 months! http://ads.osdn.com/?ad_id%62&alloc_ida84&op=click _______________________________________________ Linux-hotplug-devel mailing list http://linux-hotplug.sourceforge.net Linux-hotplug-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-hotplug-devel