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. > > Arnd -- With Best Regards, Andy Shevchenko -- 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
