On Mon, 2019-02-25 at 15:54 -0800, Evan Green wrote: > On Mon, Dec 31, 2018 at 8:52 PM Yong Wu <yong.wu@xxxxxxxxxxxx> wrote: > > > > The iommu consumer should use device_link to connect with the > > smi-larb(supplier). then the smi-larb should run before the iommu > > consumer. Here we delay the iommu driver until the smi driver is > > ready, then all the iommu consumer always is after the smi driver. > > > > When there is no this patch, if some consumer drivers run before > > smi-larb, the supplier link_status is DL_DEV_NO_DRIVER(0) in the > > device_link_add, then device_links_driver_bound will use WARN_ON > > to complain that the link_status of supplier is not right. > > > > I don't quite have enough knowledge of device links to figure out if > this is a) the right fix, b) a deficiency in the device_links code, or > c) neither. I can not say more about the device link, But from the MTK iommu point of view, it looks a right fix. As the comment above, we should make sure the probe sequence, SMI-larb should be before MTK IOMMU which need be before iommu-consumer. this patch help SMI-larb always is before MTK_IOMMU. Then if there is no this patchset, what the MTK_IOMMU will happen?. The MTK_IOMMU is subsys_initcall, all the consume only need after the MTK_IOMMU and don't need wait for SMI-larb driver. If some consume run before SMI-larb driver, It also is OK while it don't call mtk_smi_larb_get in this probe.(Of course it will abort if it call this while smi-driver don't probe at that time). the consumer and smi-larb normally are module_init, we can not guarantee the the sequence. it is a potential issue. Some consume know it should wait for SMI-larb like [1], but It don't work. [1] https://elixir.bootlin.com/linux/v5.0-rc1/source/drivers/media/platform/mtk-mdp/mtk_mdp_comp.c#L145 > > Perhaps someone else could chime in on this one. > -Evan > > _______________________________________________ > Linux-mediatek mailing list > Linux-mediatek@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-mediatek
