Message ID | 1430856611-10487-1-git-send-email-eric@anholt.net |
---|---|
State | New |
Headers | show |
On Tue, 05 May 2015, Eric Anholt wrote: > There exists a tiny MMU, configurable only by the VC (running the > closed firmware), which maps from the ARM's physical addresses to bus > addresses. These bus addresses determine the caching behavior in the > VC's L1/L2 (note: separate from the ARM's L1/L2) according to the top > 2 bits. The bits in the bus address mean: > > From the VideoCore processor: > 0x0... L1 and L2 cache allocating and coherent > 0x4... L1 non-allocating, but coherent. L2 allocating and coherent > 0x8... L1 non-allocating, but coherent. L2 non-allocating, but coherent > 0xc... SDRAM alias. Cache is bypassed. Not L1 or L2 allocating or coherent > > From the GPU peripherals (note: all peripherals bypass the L1 > cache. The ARM will see this view once through the VC MMU): > 0x0... Do not use > 0x4... L1 non-allocating, and incoherent. L2 allocating and coherent. > 0x8... L1 non-allocating, and incoherent. L2 non-allocating, but coherent > 0xc... SDRAM alias. Cache is bypassed. Not L1 or L2 allocating or coherent > > The 2835 firmware always configures the MMU to turn ARM physical > addresses with 0x0 top bits to 0x4, meaning present in L2 but > incoherent with L1. However, any bus addresses we were generating in > the kernel to be passed to a device had 0x0 bits. That would be a > reserved (possibly totally incoherent) value if sent to a GPU > peripheral like USB, or L1 allocating if sent to the VC (like a > firmware property request). By setting dma-ranges, all of the devices > below it get a dev->dma_pfn_offset, so that dma_alloc_coherent() and > friends return addresses with 0x4 bits and avoid cache incoherency. > > This matches the behavior in the downstream 2708 kernel (see > BUS_OFFSET in arch/arm/mach-bcm2708/include/mach/memory.h). > > Signed-off-by: Eric Anholt <eric@anholt.net> > Tested-by: Noralf Trønnes <noralf@tronnes.org> > Acked-by: Stephen Warren <swarren@wwwdotorg.org> > Cc: popcornmix@gmail.com Applied, thanks. > --- > > v2: Fix length of the range from 0x1f000000 to 0x20000000, fixing the > translation for the last 16MB. > > arch/arm/boot/dts/bcm2835.dtsi | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi > index eb33a8c..3c899b3 100644 > --- a/arch/arm/boot/dts/bcm2835.dtsi > +++ b/arch/arm/boot/dts/bcm2835.dtsi > @@ -15,6 +15,7 @@ > #address-cells = <1>; > #size-cells = <1>; > ranges = <0x7e000000 0x20000000 0x02000000>; > + dma-ranges = <0x40000000 0x00000000 0x20000000>; > > timer@7e003000 { > compatible = "brcm,bcm2835-system-timer";
diff --git a/arch/arm/boot/dts/bcm2835.dtsi b/arch/arm/boot/dts/bcm2835.dtsi index eb33a8c..3c899b3 100644 --- a/arch/arm/boot/dts/bcm2835.dtsi +++ b/arch/arm/boot/dts/bcm2835.dtsi @@ -15,6 +15,7 @@ #address-cells = <1>; #size-cells = <1>; ranges = <0x7e000000 0x20000000 0x02000000>; + dma-ranges = <0x40000000 0x00000000 0x20000000>; timer@7e003000 { compatible = "brcm,bcm2835-system-timer";