The Broadcom SiByte BCM1250, BCM1125, and BCM1125H SOCs have an onchip
DRAM controller that supports memory amounts of up to 16GiB, and due to
how the address decoder has been wired in the SOC any memory beyond 1GiB
is actually mapped starting from 4GiB physical up, that is beyond the
32-bit addressable limit[1]. Consequently if the maximum amount of
memory has been installed, then it will span up to 19GiB.
Many of the evaluation boards we support that are based on one of these
SOCs have their memory soldered and the amount present fits in the
32-bit address range. The BCM91250A SWARM board however has actual DIMM
slots and accepts, depending on the peripherals revision of the SOC, up
to 4GiB or 8GiB of memory in commercially available JEDEC modules[2].
I believe this is also the case with the BCM91250C2 LittleSur board.
This means that up to either 3GiB or 7GiB of memory requires 64-bit
addressing to access.
I believe the BCM91480B BigSur board, which has the BCM1480 SOC instead,
accepts at least as much memory, although I have no documentation or
actual hardware available to verify that.
Both systems have PCI slots installed for use by any PCI option boards,
including ones that only support 32-bit addressing (additionally the
32-bit PCI host bridge of the BCM1250, BCM1125, and BCM1125H SOCs limits
addressing to 32-bits), and there is no IOMMU available. Therefore for
PCI DMA to work in the presence of memory beyond enable swiotlb for the
affected systems.
All the other SOC onchip DMA devices use 40-bit addressing and therefore
can address the whole memory, so only enable swiotlb if PCI support and
support for DMA beyond 4GiB have been both enabled in the configuration
of the kernel.
This shows up as follows:
Broadcom SiByte BCM1250 B2 @ 800 MHz (SB1 rev 2)
Board type: SiByte BCM91250A (SWARM)
Determined physical RAM map:
memory: 000000000fe7fe00 @ 0000000000000000 (usable)
memory: 000000001ffffe00 @ 0000000080000000 (usable)
memory: 000000000ffffe00 @ 00000000c0000000 (usable)
memory: 0000000087fffe00 @ 0000000100000000 (usable)
software IO TLB: mapped [mem 0xcbffc000-0xcfffc000] (64MB)
in the bootstrap log and removes failures like these:
defxx 0000:02:00.0: dma_direct_map_page: overflow 0x0000000185bc6080+4608 of device mask ffffffff bus mask 0
fddi0: Receive buffer allocation failed
fddi0: Adapter open failed!
IP-Config: Failed to open fddi0
defxx 0000:09:08.0: dma_direct_map_page: overflow 0x0000000185bc6080+4608 of device mask ffffffff bus mask 0
fddi1: Receive buffer allocation failed
fddi1: Adapter open failed!
IP-Config: Failed to open fddi1
when memory beyond 4GiB is handed out to devices that can only do 32-bit
addressing.
This updates commit cce335ae47e2 ("[MIPS] 64-bit Sibyte kernels need
DMA32.").
References:
[1] "BCM1250/BCM1125/BCM1125H User Manual", Revision 1250_1125-UM100-R,
Broadcom Corporation, 21 Oct 2002, Section 3: "System Overview",
"Memory Map", pp. 34-38
[2] "BCM91250A User Manual", Revision 91250A-UM100-R, Broadcom
Corporation, 18 May 2004, Section 3: "Physical Description",
"Supported DRAM", p. 23
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
References: cce335ae47e2 ("[MIPS] 64-bit Sibyte kernels need DMA32.")
---
Changes from v2:
- missing reference to [1] added.
Changes from v1:
- title updated to include LittleSur.
---
arch/mips/Kconfig | 3 +++
arch/mips/sibyte/common/Makefile | 1 +
arch/mips/sibyte/common/dma.c | 19 +++++++++++++++++++
3 files changed, 23 insertions(+)
linux-mips-sibyte-swiotlb.diff
Index: linux-20181104-swarm64-eb/arch/mips/Kconfig
===================================================================
--- linux-20181104-swarm64-eb.orig/arch/mips/Kconfig
+++ linux-20181104-swarm64-eb/arch/mips/Kconfig
@@ -794,6 +794,7 @@ config SIBYTE_SWARM
select SYS_SUPPORTS_HIGHMEM
select SYS_SUPPORTS_LITTLE_ENDIAN
select ZONE_DMA32 if 64BIT
+ select SWIOTLB if ARCH_DMA_ADDR_T_64BIT && PCI
config SIBYTE_LITTLESUR
bool "Sibyte BCM91250C2-LittleSur"
@@ -805,6 +806,7 @@ config SIBYTE_LITTLESUR
select SYS_SUPPORTS_BIG_ENDIAN
select SYS_SUPPORTS_HIGHMEM
select SYS_SUPPORTS_LITTLE_ENDIAN
+ select SWIOTLB if ARCH_DMA_ADDR_T_64BIT && PCI
config SIBYTE_SENTOSA
bool "Sibyte BCM91250E-Sentosa"
@@ -826,6 +828,7 @@ config SIBYTE_BIGSUR
select SYS_SUPPORTS_HIGHMEM
select SYS_SUPPORTS_LITTLE_ENDIAN
select ZONE_DMA32 if 64BIT
+ select SWIOTLB if ARCH_DMA_ADDR_T_64BIT && PCI
config SNI_RM
bool "SNI RM200/300/400"
Index: linux-20181104-swarm64-eb/arch/mips/sibyte/common/Makefile
===================================================================
--- linux-20181104-swarm64-eb.orig/arch/mips/sibyte/common/Makefile
+++ linux-20181104-swarm64-eb/arch/mips/sibyte/common/Makefile
@@ -1,4 +1,5 @@
obj-y := cfe.o
+obj-$(CONFIG_SWIOTLB) += dma.o
obj-$(CONFIG_SIBYTE_BUS_WATCHER) += bus_watcher.o
obj-$(CONFIG_SIBYTE_CFE_CONSOLE) += cfe_console.o
obj-$(CONFIG_SIBYTE_TBPROF) += sb_tbprof.o
Index: linux-20181104-swarm64-eb/arch/mips/sibyte/common/dma.c
===================================================================
--- /dev/null
+++ linux-20181104-swarm64-eb/arch/mips/sibyte/common/dma.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * DMA support for Broadcom SiByte platforms.
+ *
+ * Copyright (c) 2018 Maciej W. Rozycki
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/swiotlb.h>
+#include <asm/bootinfo.h>
+
+void __init plat_swiotlb_setup(void)
+{
+ swiotlb_init(1);
+}
