NOTE: This patch builds upon Stefan's series providing basic support for RPi4[1]. I'm mostly interested in verifying if this is the correct approach to the issue stated below. If so I assume this will be added to Stefan's v2 series.
The new Raspberry Pi 4 happens to have weird DMA constraints. Even though it might contain up to 4 GB of ram, most devices can only access the first lower GB of memory. This breaks the overall assumption DMA API makes whereas 32-bit DMA masks are always supported[2], and potentially breaks DMA addressing for all streaming DMA users. This has already been observed with 'sdhci-iproc' but might as well happen elsewhere. Note that contiguous allocations are safe as 'dma_zone_size' is set accordingly. To get around that limitation we register arm's dmabounce dma-ops on all devices hooked to the SoC's main interconnect. [1] https://www.spinics.net/lists/arm-kernel/msg742120.html [2] https://www.spinics.net/lists/arm-kernel/msg742736.html Signed-off-by: Nicolas Saenz Julienne <nsaenzjulie...@suse.de> --- arch/arm/mach-bcm/Kconfig | 1 + arch/arm/mach-bcm/board_bcm2835.c | 29 +++++++++++++++++++++++++++++ 2 files changed, 30 insertions(+) diff --git a/arch/arm/mach-bcm/Kconfig b/arch/arm/mach-bcm/Kconfig index 5e5f1fabc3d4..588326f7e269 100644 --- a/arch/arm/mach-bcm/Kconfig +++ b/arch/arm/mach-bcm/Kconfig @@ -168,6 +168,7 @@ config ARCH_BCM2835 select PINCTRL select PINCTRL_BCM2835 select MFD_CORE + select DMABOUNCE if ARCH_MULTI_V7 help This enables support for the Broadcom BCM2835 and BCM2836 SoCs. This SoC is used in the Raspberry Pi and Roku 2 devices. diff --git a/arch/arm/mach-bcm/board_bcm2835.c b/arch/arm/mach-bcm/board_bcm2835.c index c09cf25596af..7aff29f77ca7 100644 --- a/arch/arm/mach-bcm/board_bcm2835.c +++ b/arch/arm/mach-bcm/board_bcm2835.c @@ -3,6 +3,8 @@ * Copyright (C) 2010 Broadcom */ +#include <linux/device.h> +#include <linux/dma-mapping.h> #include <linux/init.h> #include <linux/irqchip.h> #include <linux/of_address.h> @@ -24,8 +26,35 @@ static const char * const bcm2835_compat[] = { NULL }; +static int bcm2835_needs_bounce(struct device *dev, dma_addr_t dma_addr, size_t size) +{ + /* + * The accepted dma addresses are [0xc0000000, 0xffffffff] which map to + * ram's [0x00000000, 0x3fffffff]. + */ + return dma_addr < 3ULL * SZ_1G; +} + +static int bcm2835_platform_notify(struct device *dev) +{ + if (dev->parent && !strcmp("soc", dev_name(dev->parent))) { + dev->dma_mask = &dev->coherent_dma_mask; + dev->coherent_dma_mask = DMA_BIT_MASK(30); + dmabounce_register_dev(dev, 2048, 4096, bcm2835_needs_bounce); + } + + return 0; +} + +void __init bcm2835_init_early(void) +{ + if(of_machine_is_compatible("brcm,bcm2711")) + platform_notify = bcm2835_platform_notify; +} + DT_MACHINE_START(BCM2835, "BCM2835") .dma_zone_size = SZ_1G, .dt_compat = bcm2835_compat, .smp = smp_ops(bcm2836_smp_ops), + .init_early = bcm2835_init_early, MACHINE_END -- 2.22.0
