| Message ID | Pine.LNX.4.64.1401281420580.2714@axis700.grange |
|---|---|
| State | New |
| Headers | show |
On Tue, 28 Jan 2014, Guennadi Liakhovetski wrote: > Hi Michal, > > (trimmed CC a bit) > > On Mon, 27 Jan 2014, Michal Simek wrote: > > > On 01/27/2014 06:52 PM, Russell King - ARM Linux wrote: > > > On Mon, Jan 27, 2014 at 06:45:50PM +0100, Michal Simek wrote: > > >> Why 0x4000? IRC Linux for ARM is using space for any purpose. > > >> Russell knows this much better than I. > > > > > > Probably because as the kernel is loaded at 0x8000, it will place the > > > swapper page table at 0x4000, thus covering from 0x4000 upwards. > > > > Ah yeah swapper. > > > > > > > > Thus, the majority of your un-DMA-able memory will be kernel text or > > > swapper page tables. > > > > Yes, exactly. > > 0x0 - 0x4000 - reserving not to be used by DMA > > 0x4000 - 0x8000 swapper page table > > 0x8000 - 0x80000 kernel text + up > > Maybe you could submit something like the attached patch upstream. I'm not > sure shom you'd like to put as its original author. I put John Linn there > as he originally authored commit 5b9f3f2ac8a3e4edae9de7b855f25f757884d84c Sorry, I actually meant commit 83e198c01c381a1d90ba07e241a517d1dabf7c84 Guennadi > from Xilinx tree with the same description, as the attached patch. > Unfortunately, that commit didn't have an Sob. --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/
On Tue, Jan 28, 2014 at 02:28:28PM +0100, Guennadi Liakhovetski wrote: > +static void __init zynq_memory_init(void) > +{ > + /* > + * Reserve the 0-0x4000 addresses (before page tables and kernel) > + * which can't be used for DMA > + */ > + if (!__pa(PAGE_OFFSET)) > + memblock_reserve(0, 0x4000); Or maybe this: memblock_reserve(__pa(PAGE_OFFSET), __pa(swapper_pg_dir)); since that's actually what you mean here.
On 01/28/2014 02:48 PM, Russell King - ARM Linux wrote: > On Tue, Jan 28, 2014 at 02:28:28PM +0100, Guennadi Liakhovetski wrote: >> +static void __init zynq_memory_init(void) >> +{ >> + /* >> + * Reserve the 0-0x4000 addresses (before page tables and kernel) >> + * which can't be used for DMA >> + */ >> + if (!__pa(PAGE_OFFSET)) >> + memblock_reserve(0, 0x4000); > > Or maybe this: > > memblock_reserve(__pa(PAGE_OFFSET), __pa(swapper_pg_dir)); > > since that's actually what you mean here. yep with that if too. I will prepare that patch and will send it out. Thanks, Michal
On Tue, Jan 28, 2014 at 01:48:27PM +0000, Russell King - ARM Linux wrote: > On Tue, Jan 28, 2014 at 02:28:28PM +0100, Guennadi Liakhovetski wrote: > > +static void __init zynq_memory_init(void) > > +{ > > + /* > > + * Reserve the 0-0x4000 addresses (before page tables and kernel) > > + * which can't be used for DMA > > + */ > > + if (!__pa(PAGE_OFFSET)) > > + memblock_reserve(0, 0x4000); > > Or maybe this: > > memblock_reserve(__pa(PAGE_OFFSET), __pa(swapper_pg_dir)); > > since that's actually what you mean here. Can you have a non-zero PAGE_OFFSET and swapper_pg_dir != 0x4000? Crash dump kernel maybe? Perhaps: if (__pa(PAGE_OFFSET) < 0x8000) memblock_reserve(__pa(PAGE_OFFSET), min(__pa(swapper_pg_dir), 0x8000)); ? The Zynq TRM, UG585 pg 115, describes this issue. Physical addresses below 0x8000 are not accessible to DMA from the AXI interconnect. Though, how does a crash dump kernel know it needs to bounce buffer the swapper if it dumps it via DMA? Regards, Jason
From d00684a6d899048938086c11185c89f082b881e0 Mon Sep 17 00:00:00 2001 From: John Linn <john.linn@xilinx.com> Date: Tue, 28 Jan 2014 14:06:45 +0100 Subject: [PATCH] Xilinx: ARM: BSP: prevent DMA into lower memory The DMA zone from 2.6.39 is no longer supported such that a new method was needed. The old method was lost in the move to 3.0 and USB was seeing failures. Signed-off-by: Michal Simek <michal.simek@xilinx.com> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de> --- arch/arm/mach-zynq/common.c | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-) diff --git a/arch/arm/mach-zynq/common.c b/arch/arm/mach-zynq/common.c index 9a7bd13..2d51453 100644 --- a/arch/arm/mach-zynq/common.c +++ b/arch/arm/mach-zynq/common.c @@ -25,6 +25,7 @@ #include <linux/of_irq.h> #include <linux/of_platform.h> #include <linux/of.h> +#include <linux/memblock.h> #include <asm/mach/arch.h> #include <asm/mach/map.h> @@ -39,6 +40,22 @@ void __iomem *zynq_scu_base; +/** + * zynq_memory_init() - Initialize special memory + * + * We need to stop things allocating the low memory as DMA can't work in + * the 1st 512K of memory. Using reserve vs remove is not totally clear yet. + */ +static void __init zynq_memory_init(void) +{ + /* + * Reserve the 0-0x4000 addresses (before page tables and kernel) + * which can't be used for DMA + */ + if (!__pa(PAGE_OFFSET)) + memblock_reserve(0, 0x4000); +} + static struct of_device_id zynq_of_bus_ids[] __initdata = { { .compatible = "simple-bus", }, {} @@ -113,5 +130,6 @@ DT_MACHINE_START(XILINX_EP107, "Xilinx Zynq Platform") .init_machine = zynq_init_machine, .init_time = zynq_timer_init, .dt_compat = zynq_dt_match, + .reserve = zynq_memory_init, .restart = zynq_system_reset, MACHINE_END -- 1.7.2.5