Hi Nicolas, On 27.04.2020 12:15, Nicolas Saenz Julienne wrote: > On Fri, 2020-04-24 at 18:50 +0200, Sylwester Nawrocki wrote: >> This patch adds basic driver for the Broadcom STB PCIe host controller. >> The code is based on Linux upstream driver (pcie-brcmstb.c) with MSI >> handling removed. The inbound access memory region is not currently >> parsed from dma-ranges DT property and a fixed 4GB region is used. >> >> The patch has been tested on RPI4 board, i.e. on BCM2711 SoC with VL805 >> USB Host Controller. >> >> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulie...@suse.de> >> Signed-off-by: Sylwester Nawrocki <s.nawro...@samsung.com> >> --- >> Changes since RFC: >> - reworked to align with current Linux mainline version and u-boot driver >> by Nicolas Saenz Julienne > [...] > >> + >> + /* >> + * TODO: Use the base address and size(s) provided in the dma-ranges >> + * property. >> + */ >> + rc_bar2_offset = 0; >> + rc_bar2_size = 1ULL << 32; > From experience this works fine, although it highly depends on how DMA > memory is > handled in u-boot. > > For example, in arm64 Linux, DMA memory was allocated from ZONE_DMA32, which > would return memory smaller than 4GB. This was not good enough for bcm2711b0 > -- > revision b0 of rpi4's SoC, so far the most common out there -- which has an > internal wiring bug that prevents PCIe from accessing memory higher than 3GB > (RPi4 might have up to 4GB). So we had to introduce a ZONE_DMA, which covers > the lower GB of memory, in order to allocate suitable DMA memory for PCI and > other DMA limited devices. > > While playing around with u-boot's xHCI I saw that all memory is allocated is > located in the lower 1GB. But never got to look into why. I'm curious to know > if someone knows how's that handled in u-boot. Ultimately, depending on how it > works, we might be able to just disregard dma-ranges altogether. > > For some extra context xhci_malloc() gets its memory from memalign(). And it's > not clear to me how that function decides which memory to use.
I think that memalign() allocates memory from the uboot's defined SDRAM (from its end). Assuming that CONFIG_SYS_SDRAM_SIZE is set to 128M in include/configs/rpi.h it should be always safe, but I will check that tomorrow to be 100% sure. Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
