Re: [PATCH/RFC] Call platform_notify_remove later

[Len Brown <len.brown@intel.com>]

On Tuesday 17 October 2006 22:08, Benjamin Herrenschmidt wrote:
> (CC'ed Deepak and Len, the two only users of that callback I could find
> in the tree).
> 
> Right now, the driver core calls the platform_notify hook when adding a
> device, before attaching to the bus and probing drivers. That is all
> good. However, it calls platform_notify_remove on removal of a device
> also -before- calling bus_remove_device(), and thus before unhooking
> drivers from that device. That strikes me as odd, and even incorrect.

AFAICS, your change is logical and should be fine.

thanks,
-Len

> In my case, I want to maintain an arch-wide data structure attached to
> every struct device in the system (currently pointed to by firmware_data
> though I'd like another field, but that's a separate discussion). I need
> that among others, to hold the DMA ops and pointer to the right iommu
> for this device since our current code testing for all sorts of known
> bus types is just a total mess.
> 
> For bus types I have complete control of, like powerpc VIO or EBUS, I
> can control creation and destruction of this data structure within the
> bus specific code, that's all good. But that's not the case for PCI (or
> by extension, any other bus type that supports DMA that we might come up
> with and that isn't platform specific).
> 
> Thus I want to use those platform_notify and platform_notify_remove
> hooks in order to maintain that data structure for those bus types. The
> problem is that in the case of removal, my remove call back will be
> called before the driver remove, and thus with the driver potentially
> still operating, using the DMA ops, etc...
> 
> I don't see any reason why this is done that way, so I'm proposing to
> just move the call down a bit. I can then cleanup the data structure and
> pointers after the driver remove() returns, which is safer.
> 
> It's still not perfect. Best would have been a platform_notify_destroy
> hook in the actual freeing of the kobject, but there is no common
> routine for that, or there is one but it's not used by all bus types.
> PCI doesn't use it for example, thus that hook would have to be added
> all over the place which I'm not too keen to do right now. Especially
> since as far as I can tell, for my need (DMA ops), return from driver
> remove() should be just fine.
> 
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
> 
> (Note: This isn't 2.6.19 material of course, though I'm cooking a pile
> of patches relying on that for 2.6.20 so please let me know if I'm on
> the wrong track asap :-)
> 
> Index: linux-cell/drivers/base/core.c
> ===================================================================
> --- linux-cell.orig/drivers/base/core.c	2006-10-06 13:48:02.000000000 +1000
> +++ linux-cell/drivers/base/core.c	2006-10-18 11:53:50.000000000 +1000
> @@ -608,12 +608,13 @@ void device_del(struct device * dev)
>  	device_remove_groups(dev);
>  	device_remove_attrs(dev);
>  
> +	bus_remove_device(dev);
> +
>  	/* Notify the platform of the removal, in case they
>  	 * need to do anything...
>  	 */
>  	if (platform_notify_remove)
>  		platform_notify_remove(dev);
> -	bus_remove_device(dev);
>  	device_pm_remove(dev);
>  	kobject_uevent(&dev->kobj, KOBJ_REMOVE);
>  	kobject_del(&dev->kobj);
> 
> 
> -
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