From: 이왕석 <wangseok.lee@xxxxxxxxxxx> Date: Wed, 30 Mar 2022 12:52:03 +0900 > > --------- Original Message --------- > > Sender : Alexander Lobakin <alexandr.lobakin@xxxxxxxxx> > > Date : 2022-03-28 23:34 (GMT+9) > > Title : Re: [PATCH] PCI: dwc: Modify the check about MSI DMA mask 32-bit > > > > From: 이왕석 <wangseok.lee@xxxxxxxxxxx> > > Date: Mon, 28 Mar 2022 11:30:09 +0900 > > > >> If dma_mask is more than 32 bits this will trigger an error occurs when > >> dma_map_single_attrs() is performed. > >> > >> dma_map_single_attrs() -> dma_map_page_attrs()-> > >> error return in dma_direct_map_page(). > >> > >> On ARTPEC-8, this fails with: > >> artpec8-pcie 17200000.pcie: DMA addr 0x0000000106b052c8+2 overflow > >> (mask ffffffff, bus limit 27fffffff) > > > > Isn't it a bug in the platform DMA code? dma_set_mask(32) > > explicitly says that the system *must not* give DMA addresses wider > > than 32 bits. If the system can't satisfy this requirement, then it > > should return failure on dma_set_mask(32) -- this way you will only > > get the corresponding warning, but there'll be no overflows (as the > > mask will not be changed). > > The idea of this call is to try to avoid getting 33+ bit mappings > > so that PCI controllers which support only 32-bit masks could still > > work correctly on the 64-bit systems. If the call fails, then this > > message gets printed that you've been warned and it's your > > responsibility to make sure that the controller won't get truncated > > addresses. Having the call succeeded and then 33+ bit DMA addresses > > is wrong. > > > > Please correct me if I'm wrong. > > > > Hello, Alexander Lobakin > Thanks for your review. > > You are right. > My concern is that case of trying to use 33+bit dma mappings on > 64bit system. > It is about the call sequence of the functions related to dma > setting, not the operation of the dma_set_mask() function. > If dma_set_mask(33+) is performed before dw_pcie_host_init() > for using 33+bit dma mapping, following error occurs > in dma_map_single_attrs() > ex) DMA addr 0x0000000106b052c8+2 overflow > (mask ffffffff, bus limit 27fffffff) > dma_set_mask(33+) -> dw_pcie_host_init(): dma_set_mask(32) -> > dma_map_single_attrs() -> > error return in dma_direct_map_page(): > because dma addr is 33+ but masking value is 32 > > So if the user has already set dma_mask to 33+ in order to use 33+, > i suggested to modify dma_set_mask(32) not to be called. > > Please let me know your opinion. I'm not super familiar with the DMA internals, so adding Chris here, maybe he'd like to comment, but anyway, the lower/arch layer must not give the DMA addresses wider than the number of bits passed to dma_set_mask() if that call returned 0. > > Thank you. --- 8< --- > >> -- > >> 2.9.5 > > > > Thanks, > > Al Thanks, Al
