Hello Yong, On Mon, Sep 14, 2015 at 01:25:00PM +0100, Yong Wu wrote: > On Tue, 2015-07-21 at 18:11 +0100, Will Deacon wrote: > > > + ret = _arm_short_map(data, iova, paddr, pgdprot, pteprot, large); > > > + > > > + tlb->tlb_add_flush(iova, size, true, data->iop.cookie); > > > + tlb->tlb_sync(data->iop.cookie); > > > > In _arm_short_map, it looks like you can only go from invalid -> valid, > > so why do you need to flush the TLB here? > > Hi Will, > Here is about flush-tlb after map iova, I have deleted it in v4 > following this suggestion. But We meet a problem about it. Ok. > Take a example with JPEG. the test steps is: > a).JPEG HW decode a picture with the source iova,like 0xfd780000. > b).JPEG HW decode done, It will unmap the iova(write 0 in pagetable and > flush tlb). > c).JPEG HW decode the second picture, whose source iova is also > 0xfd780000. > Then our HW maybe fail due to it will auto prefetch, It may prefecth > between the step b) and c). then the HW may fetch the pagetable content > which has been unmapped in step b). then the HW will get the iova's > physical address is 0, It will translation fault! Oh no! So-called "negative caching" is certainly prohibited by the ARM architecture, but if you've built it then we can probably work around it as an additional quirk. I assume the prefetcher stops prefetching when it sees an invalid descriptor? > So I think our HW need flush-tlb after map iova. Could we add a > QUIRK like "IO_PGTABLE_QUIRK_AUTO_PREFETCH_ENABLE" for it? > If it's not allowed, we will have to add this in our internal function > mtk_iommu_map of mtk_iommu.c. Actually, this type of quirk is ringing bells with me (I think another IOMMU needed something similar in the past), so maybe just add IO_PGTABLE_QUIRK_TLBI_ON_MAP? Will -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
