* Tero Kristo <tero.kristo@xxxxxxxxx> [081211 07:58]: > From: Paul Walmsley <paul@xxxxxxxxx> > > Mark the SRAM (aka OCM RAM) as Non-cacheable Normal memory[1]. This > is to prevent the ARM from evicting existing cache lines to SDRAM > while code is executing from the SRAM. Necessary since one of the > primary uses for the SRAM is to hold the code and data for the CORE > DPLL M2 divider reprogramming code, which must execute while the SDRC > is idled. If the ARM attempts to write cache lines back to the while > the SRAM code is running, the ARM will stall[2]. > > TI deals with this problem in the CDP kernel by marking the SRAM as > Strongly-ordered memory. > > Tero Kristo <tero.kristo@xxxxxxxxx> caught a bug in an earlier version of > this patch - thanks Tero. As I talked with Paul, we might want to set up two sections in SRAM. One section that is cached and another that is not. Tony > > ... > > 1. ARMv7 ARM (DDI 0406A) pp. A3-30, A3-31, B3-32. > > 2. Private communication with Richard Woodruff <r-woodruff2@xxxxxx> > > Signed-off-by: Paul Walmsley <paul@xxxxxxxxx> > Cc: Tero Kristo <tero.kristo@xxxxxxxxx> > Cc: Richard Woodruff <r-woodruff2@xxxxxx> > --- > arch/arm/plat-omap/sram.c | 9 +++++++++ > 1 files changed, 9 insertions(+), 0 deletions(-) > mode change 100755 => 100644 arch/arm/plat-omap/sram.c > > diff --git a/arch/arm/plat-omap/sram.c b/arch/arm/plat-omap/sram.c > old mode 100755 > new mode 100644 > index abcc05b..04214e1 > --- a/arch/arm/plat-omap/sram.c > +++ b/arch/arm/plat-omap/sram.c > @@ -207,6 +207,15 @@ void __init omap_map_sram(void) > base = OMAP3_SRAM_PA; > base = ROUND_DOWN(base, PAGE_SIZE); > omap_sram_io_desc[0].pfn = __phys_to_pfn(base); > + > + /* > + * SRAM must be marked as non-cached on OMAP3 since the > + * CORE DPLL M2 divider change code (in SRAM) runs with the > + * SDRAM controller disabled, and if it is marked cached, > + * the ARM may attempt to write cache lines back to SDRAM > + * which will cause the system to hang. > + */ > + omap_sram_io_desc[0].type = MT_MEMORY_NONCACHED; > } > > omap_sram_io_desc[0].length = 1024 * 1024; /* Use section desc */ > -- > 1.5.4.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-omap" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
