On Wednesday 18 November 2015 11:35:27 Andy Shevchenko wrote: > On Fri, Nov 13, 2015 at 11:35 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Friday 13 November 2015 03:10:13 Andy Shevchenko wrote: > >> On Thu, Nov 12, 2015 at 4:14 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > >> > The dw_mmc driver stores the physical address of the MMIO registers > >> > in a pointer, which requires the use of type casts, and is actually > >> > broken if anyone ever has this device on a 32-bit SoC in registers > >> > above 4GB. Gcc warns about this possibility when the driver is built > >> > with ARM LPAE enabled: > >> > >> > - host->phy_regs = (void *)(regs->start); > >> > + host->phy_regs = regs->start; > >> > >> > /* Set external dma config: burst size, burst width */ > >> > - cfg.dst_addr = (dma_addr_t)(host->phy_regs + fifo_offset); > >> > + cfg.dst_addr = host->phy_regs + fifo_offset; > >> > >> dst_addr is dma_addr_t? > > > > Sort of. It doesn't really fit into any of the categories, and we actually > > had a patch to change the type in the past, see > > https://lkml.org/lkml/2015/7/10/167. Not sure what is going on there. > > > >> > /* Registers's physical base address */ > >> > - void *phy_regs; > >> > + resource_size_t phy_regs; > >> > >> If dst_addr is dma_addr_t wouldn't be a problem when > >> resource_size_t is defined as 64-bit address, and dma_addr_t as 32-bit? > >> > >> Btw, for me casting to dma_addr_t looks sane. > > > > The background here is that the address comes from a resource_size_t > > that describes the MMIO register area as seen from the CPU, and that > > is normally a phys_addr_t (resource_size_t is defined as being long > > enough to store a phys_addr_t or various other things depending on > > resource->flags). > > > > dma_addr_t strictly speaking refers to a RAM location as seen by a > > DMA master, and that only comes out of dma_map_*() or > > dma_alloc_coherent(). > > > > The DMA engine wants something else here, which is an MMIO register > > address as seen by a DMA master, and we don't have a separate typedef > > for that. Almost universally all of resource_size_t, phys_addr_t and > > dma_addr_t are the same type, and if we ever get a platform that > > wants something other than a phys_addr_t to put into cfg.dst_addr, > > we are in deep trouble. > > DMA operates with address space covered by dma_addr_t, if you use > phys_addr_t you may get address out of DMA boundaries. This is should > be done in hardware / firmware / platform representation. > So, I don't see any reason not to use dma_addr_t here. As I said above, this isn't really the same as DMA: all normal dma_addr_t are returned from dma_alloc_* or dma_map_*, point to RAM and might go trhough an IOMMU, all of which is not true here, hence the patch to change the type to phys_addr_t. You really can't get out of bounds because the data comes from a phys_addr_t and refers to a fixed location in hardware. If a platform has registers higher than a 32-bit address, its phys_addr_t must be 64-bit, but its dma_addr_t not necessarily so (even though the two are the same almost always in practice). Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
