On Tue, Oct 18, 2011 at 11:18 AM, Olof Johansson <olof@xxxxxxxxx> wrote: > From: Jon Mayo <jmayo@xxxxxxxxxx> > > Tegra2 hangs if APB registers are accessed from the cpu during an > apb dma operation. The workaround is to use apb dma to read/write the > registers instead. > > There is a dependency loop between fuses, clocks, and APBDMA. If dma > is enabled, fuse reads must go through APBDMA to avoid corruption due > to a hw bug. APBDMA requires a clock to be enabled. Clocks must read > a fuse to determine allowable cpu frequencies. > > Separate out the fuse DMA initialization, and allow the fuse read > and write functions to be called without using DMA before the DMA > initialization has been completed. Access to the fuses before APBDMA > is initialized won't hit the hardware bug because nothing else can be > using DMA. > > Original fuse registar access code from Varun Wadekar > <vwadekar@xxxxxxxxxx>, improved by Colin Cross <ccross@xxxxxxxxxxx> > and later moved to separate driver by Jon Mayo <jmayo@xxxxxxxxxx>. > > Signed-off-by: Jon Mayo <jmayo@xxxxxxxxxx> > [olof: hooked up init calls to dma init, minor cleanups] > Signed-off-by: Olof Johansson <olof@xxxxxxxxx> > --- > arch/arm/mach-tegra/Makefile | 1 + > arch/arm/mach-tegra/apbio.c | 149 ++++++++++++++++++++++++++++++++++++++++++ > arch/arm/mach-tegra/apbio.h | 22 ++++++ > arch/arm/mach-tegra/dma.c | 4 + > 4 files changed, 176 insertions(+), 0 deletions(-) > create mode 100644 arch/arm/mach-tegra/apbio.c > create mode 100644 arch/arm/mach-tegra/apbio.h > <snip> > diff --git a/arch/arm/mach-tegra/dma.c b/arch/arm/mach-tegra/dma.c > index c0cf967..b7b6957 100644 > --- a/arch/arm/mach-tegra/dma.c > +++ b/arch/arm/mach-tegra/dma.c > @@ -33,6 +33,8 @@ > #include <mach/iomap.h> > #include <mach/suspend.h> > > +#include "apbio.h" > + > #define APB_DMA_GEN 0x000 > #define GEN_ENABLE (1<<31) > > @@ -735,6 +737,8 @@ int __init tegra_dma_init(void) > > tegra_dma_initialized = true; > > + tegra_init_apb_dma(); > + It seems wrong for the dma api init to call init on one of the users of the dma api. For explicit ordering dependencies like this, maybe postcore_initcall is not the right way to trigger tegra_dma_init. > return 0; > fail: > writel(0, addr + APB_DMA_GEN); > -- > 1.7.4.1 > > -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
