On 2020/10/23 15:17, Arnd Bergmann wrote: > On Sun, Oct 18, 2020 at 4:10 AM Leizhen (ThunderTown) > <thunder.leizhen@xxxxxxxxxx> wrote: >> On 2020/10/17 3:27, Florian Fainelli wrote: >>> On 10/16/20 11:23 AM, Arnd Bergmann wrote: >>>> On Fri, Oct 16, 2020 at 6:48 PM Florian Fainelli <f.fainelli@xxxxxxxxx> wrote: >>>>> On 10/16/20 4:01 AM, Arnd Bergmann wrote: >>>>>> On Fri, Oct 16, 2020 at 11:09 AM Zhen Lei <thunder.leizhen@xxxxxxxxxx> wrote: >>>>>>> >>>>>>> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx> >>>>>>> Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx> >>>>>> >>>>>> Acked-by: Arnd Bergmann <arnd@xxxxxxxx> >>>>>> >>>>>> I see that at least the 'bcd' and 'xhci' devices in fact try to >>>>>> use 64-bit DMA. It would be good to test this on actual >>>>>> hardware to ensure that it works correctly when this is enabled. >>>>>> >>>>>> Ideally avoiding the swiotlb bounce buffering should only >>>>>> make it faster here, but there are many chips on which >>>>>> 64-bit DMA is broken in some form. >>>>> >>>>> Is this change really an improvement though? This 'usb' pseudo bus node >>>>> could just keep being defined with #address-cells = <1> and #size-cells >>>>> = <1> so as to satisfy the 'reg' definition however we could just adjust >>>>> dma-ranges to indicate full 64-bit addressing capability. Would not that >>>>> work? >>>> >>>> When #address-cells is '1', you cannot specify dma-ranges that >>>> go beyond a 32-bit address range. >>> >>> Would not it be enough to remove the 'dma-ranges' property though? Sorry >>> for being slow here. >> >> Remove the 'dma-ranges' property should also work. After all, it is equivalent >> to the original empty dma-ranges scheme. In addition, since the IOMMU nodes are >> defined, it should be enabled. > > Are you sure? I was expecting the IOMMU not to get used here since > the devices do contain list an 'iommus' property. OK，If the SMMU maybe disabled, then your proposal is necessary. > > Arnd > > . >
