On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote: > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@xxxxxxxxxxxx> wrote: > > > > DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link > > automatically on consumer/supplier driver unbind", that means we should > > remove whole the device_link when there is no this driver no matter what > > the ref_count of the link is. > > > > CC: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx> > > --- > > The ref_count of our device_link normally is over 1. When the consumer > > device driver is removed, whole the device_link should be removed. > > Thus, I add this patch. > > --- > > I will admit to reading about device links for the first time while > reviewing this patch, but I don't really get this. Why use a kref at > all if we're just going to ignore its value? For instance, I see that > if you call device_link_add() with the same supplier and consumer, it > uses the kref to return the same link. That machinery is broken with > your change. Although I don't see any uses of it, you might also > expect a supplier or consumer could do a kref_get() on the link it got > back from device_link_add(), and have a reasonable expectation that > the link wouldn't be freed out from under it. This would also be > broken. > > Can you explain why your device_links normally have a reference count > >1, I use device link between the smi-larb device and the iommu-consumer device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this patchset, we use device_link to link the VDEC device and the smi-larb1 device in the function(mtk_iommu_config). since there are 4 ports, it will call device_link_add 4 times. > > and why those additional references can't be cleaned up in an > orderly fashion? If the iommu-consume device(like VDEC above) is removed, It should enter device_links_driver_cleanup which only ref_put one time. I guess whole the link should be removed at that time. > > (To be honest, I don't really understand the case for the AUTOREMOVE > flags at all. Is there some case where the party that set up the link > can't tear it down? Or is this a way to devm_ify the link, where devm > itself doesn't work because the links themselves stall out that > mechanism?)
