| Message ID | 1392373771-17303-7-git-send-email-linus.walleij@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Friday 14 February 2014 11:29:31 Linus Walleij wrote: > The Integrator has a custom <mach/memory.h> header defining the > BUS_OFFSET for *_to_bus and bus_to_* operations as offset from > 0x80000000. > > I have searched the documentation and cannot find any clue to > this set-up. The Integrators have no intrinsic DMA engine(s) > that need to perform any bus translations. The only thing I can > think of is the PCIv3 host found in the Integrator/AP. After > searching its documentation I cannot find any hint whatsoever > saying that it would perform DMA operations to memory offset > to 0x80000000. The PCIv3 driver does not configure anything > for DMA, and the hardware contains registers to configure > the local (CPU) side address translation. When I dump the > default values of these registers (the Linux driver does not > touch them) they contain zeroes meaning a 1-to-1 mapping to > the bus. I think this will be break bus-mastering PCI adapters. In theory any PCI add-on card can be a bus-master and write to the host memory. An offset of 0x80000000 in the PCI host is not uncommon for this. Basically what the PCI host does is forward any PCI transaction with a destination below 2GB to the PCI bus so it can target an MMIO register, and forward transactions above 2GB to the parent bus, flipping the high-order bit in the process. In the old days, we had virt_to_bus() and bus_to_virt() as interfaces for drivers to convert between a kernel pointer and an address that can be used for DMA. We have long ago (except for a handful of drivers that depend on CONFIG_TO_BUS and won't build on integrator or multiplatform) stopped using those in drivers, since the translation may be dependent on the specific device (e.g. different offsets), or may be nonlinear in case of an IOMMU. The interface that drivers use now is defined in dma-mapping.h and abstracted through dma_map_ops on ARM and some other architectures. What you need for a multiplatform kernel to work on integrator is to set the dma_map_ops for all PCI devices to an implementation that adds the correct offset. One way to do this would be to define an integrator specific dma_map_ops struct that adds a constant value for each operation and then calls into the regular arm_dma_ops. That would be an easy way out, but would not help the next person with the same problem. A more sophisticated approach, following what we did on powerpc, would be to add an offset field to struct dev_archdata and apply that in pfn_to_dma/dma_to_pfn/dma_to_virt/virt_to_dma so it gets used by all dma_map_ops implementations. For PCI devices, you probably have to copy the offset from the parent in the pcibios_add_device() function in that case, while for devices probed through DT (only the pci host bridge in this case), you have to parse the "dma_ranges" property. Arnd
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index e25419817791..c4094131314e 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -325,7 +325,6 @@ config ARCH_INTEGRATOR select HAVE_TCM select ICST select MULTI_IRQ_HANDLER - select NEED_MACH_MEMORY_H select PLAT_VERSATILE select SPARSE_IRQ select USE_OF diff --git a/arch/arm/mach-integrator/include/mach/memory.h b/arch/arm/mach-integrator/include/mach/memory.h deleted file mode 100644 index 334d5e271889..000000000000 --- a/arch/arm/mach-integrator/include/mach/memory.h +++ /dev/null @@ -1,34 +0,0 @@ -/* - * arch/arm/mach-integrator/include/mach/memory.h - * - * Copyright (C) 1999 ARM Limited - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, - * but WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA - */ -#ifndef __ASM_ARCH_MEMORY_H -#define __ASM_ARCH_MEMORY_H - -/* - * Physical DRAM offset. - */ -#define PLAT_PHYS_OFFSET UL(0x00000000) - -#define BUS_OFFSET UL(0x80000000) -#define __virt_to_bus(x) ((x) - PAGE_OFFSET + BUS_OFFSET) -#define __bus_to_virt(x) ((x) - BUS_OFFSET + PAGE_OFFSET) -#define __pfn_to_bus(x) (__pfn_to_phys(x) + (BUS_OFFSET - PHYS_OFFSET)) -#define __bus_to_pfn(x) __phys_to_pfn((x) - (BUS_OFFSET - PHYS_OFFSET)) - -#endif
The Integrator has a custom <mach/memory.h> header defining the BUS_OFFSET for *_to_bus and bus_to_* operations as offset from 0x80000000. I have searched the documentation and cannot find any clue to this set-up. The Integrators have no intrinsic DMA engine(s) that need to perform any bus translations. The only thing I can think of is the PCIv3 host found in the Integrator/AP. After searching its documentation I cannot find any hint whatsoever saying that it would perform DMA operations to memory offset to 0x80000000. The PCIv3 driver does not configure anything for DMA, and the hardware contains registers to configure the local (CPU) side address translation. When I dump the default values of these registers (the Linux driver does not touch them) they contain zeroes meaning a 1-to-1 mapping to the bus. So patch the mapping to use the kernel default. Cc: Will Deacon <will.deacon@arm.com> Cc: Jonathan Austin <jonathan.austin@arm.com> Cc: Russell King <linux@arm.linux.org.uk> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- Admittedly I'm not certain about how DMA works in PCI scenarios (only experienced with DMA engines) so some input here would be appreciated. Like if DMA support is compulory for PCI hosts or if it's somehow even unused on the PCIv3. And if someone has ever tested some DMA:ing PCI card on this machine. --- arch/arm/Kconfig | 1 - arch/arm/mach-integrator/include/mach/memory.h | 34 -------------------------- 2 files changed, 35 deletions(-) delete mode 100644 arch/arm/mach-integrator/include/mach/memory.h