linux-kernel - [PATCH] ARM: zynq: Reserve not DMAable space in front of the kernel

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Message-Id: <780bb8c8fd752eeace2fd2fbe1d8ed8572dc0d76.1391170073.git.michal.simek@xilinx.com>
Date:	Fri, 31 Jan 2014 13:08:05 +0100
From:	Michal Simek <michal.simek@...inx.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org, monstr@...str.eu,
	Josh Cartwright <josh.cartwright@...com>,
	Steffen Trumtrar <s.trumtrar@...gutronix.de>,
	Rob Herring <robherring2@...il.com>,
	Peter Crosthwaite <peter.crosthwaite@...inx.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ARM: zynq: Reserve not DMAable space in front of the kernel

Reserve space from 0x0 - __pa(swapper_pg_dir),
if kernel is loaded from 0, which is not DMAable.
It is causing problem with MMC driver and others
which want to add dma buffers to this space.

Signed-off-by: Michal Simek <michal.simek@...inx.com>
---

Jason: I don't think it is worth to bring 0x8000 magic
value and count minimum from it and phys_addr of swapper_pg_dir.
Full 512k of memory shouldn't be used by DMA.

---
 arch/arm/mach-zynq/common.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm/mach-zynq/common.c b/arch/arm/mach-zynq/common.c
index 1db2a5ca..8c09a83 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 <linux/irqchip.h>
 #include <linux/irqchip/arm-gic.h>

@@ -41,6 +42,18 @@

 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.
+ */
+static void __init zynq_memory_init(void)
+{
+	if (!__pa(PAGE_OFFSET))
+		memblock_reserve(__pa(PAGE_OFFSET), __pa(swapper_pg_dir));
+}
+
 static struct platform_device zynq_cpuidle_device = {
 	.name = "cpuidle-zynq",
 };
@@ -117,5 +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
--
1.8.2.3


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