On Wed, Apr 11, 2018 at 1:34 AM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote: > Hi Andrey, > > On Mon, Apr 09, 2018 at 09:00:52AM -0700, Andrey Smirnov wrote: >> On Tue, Apr 3, 2018 at 12:04 AM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote: >> > On Mon, Mar 26, 2018 at 06:09:15AM -0700, Andrey Smirnov wrote: >> >> In order to allow 'serdev' devices to prevent parent console device >> >> removal and correspondign memory deallocation add code to all serial >> >> driver to check result of console_unregister() and bail out early if >> >> it is unsuccessful. >> >> >> >> One example of a use-case for this would be a reset handler relying on >> >> a serdev device for transport. Without this patch underlying console >> >> device would be removed and de-allocated before reset handler is even >> >> run thus leading to unpredictable behaviour and crashes. >> > >> > Can't we make this sure at driver core level? >> >> I need to be able to prevent serial driver's "remove" function from >> ever executing to prevent any de-initialization/memory freeing from >> happening. The simplest way to solve this in driver core that comes to >> my mind is implementing simple reference counting API that children >> could use to force driver core to bail out on removing parents if they >> are still in use. Does that sound like a reasonable idea? >> >> > So if a device decides not >> > to return -EBUSY in the remove callback then the parent devices won't be >> > removed? >> >> Remove callback currently returns void, we could change it to return >> int and use it to implement a sort of implicit refcounting, but doing >> so would result in quite a bit of code churn since all of the current >> drivers would have to be converted to return int in their .remove >> callbacks. Would you rather I do this or explicit refcounting? > > Normally it helps looking at the Linux kernel to see how a problem is > solved there. Not so this time it seems. Linux distinguishes between > "remove" and "shutdown". "shutdown" is what we want during barebox > shutdown. I found a Linux driver that is similar to your situation: It > registers a restart_handler while being a i2c device itself. There seems > to be no way to prevent a device from being shutdown, it's only that the > i2c bus drivers simply do not implement it. > > Where do we go from here? I think reference counting is a bit over the > top. > > At the moment I would opt for a *very* simple solution: Let's drop the > call to console_unregister() and the freeing of resources entirely as > it gives us nothing. The only console driver I can see where removing > is valid is drivers/usb/gadget/u_serial.c and you won't use this for > restarting a SoC ;) > OK, makes sense and works for me. Will do in v2. Thanks, Andrey Smirnov _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
