On Mon, Oct 04, 2021 at 05:04:11PM +0200, Mark Kettenis wrote:
> > Date: Mon, 4 Oct 2021 13:42:48 +0000
> > From: Visa Hankala <v...@hankala.org>
> >
> > On the Zynq-7000, the lowest 512KiB of physical address space usually
> > contains RAM that is usable by the CPUs. However, many other bus
> > masters, such as the Ethernet and SDIO controllers, are not able to
> > access the 256KiB range that starts at physical address 0x40000.
> >
> > So far I have used a device tree that says that RAM starts at 0x80000,
> > to avoid the DMA hole. This is unconventional, though. Typically the
> > memory node for Zynq-7000 specifies 0x0 as the starting address for RAM.
> >
> > I think armv7 DMA constraint should be adjusted on the Zynq-7000 so that
> > less device tree customization would be needed.
> >
> > This diff makes armv7 efiboot and kernel handle the
> > openbsd,dma-constraint device tree property, with a tweak for the Zynq.
> > The code is similar to what is already present on arm64 and riscv64.
> >
> > OK?
>
> Hmm. How does Linux know it can't do DMA to that memory range?
> Normally that is done through a dma-ranges property in the device
> tree, and my idea has always been to add code to parse these
> properties to determine the valid DMA constraints. The reason there
> is special code for the rpi4 is because the initial device trees for
> the rpi4 didn't have those dma-ranges properties.
Linux reserves the first 512KiB in Zynq platform init code to prevent
the region from being used.
> I'm not necessarily against this diff going in, just curious if there
> is a better way.
>
> > Index: arch/armv7/armv7/armv7_machdep.c
> > ===================================================================
> > RCS file: src/sys/arch/armv7/armv7/armv7_machdep.c,v
> > retrieving revision 1.63
> > diff -u -p -r1.63 armv7_machdep.c
> > --- arch/armv7/armv7/armv7_machdep.c 25 Mar 2021 04:12:01 -0000
> > 1.63
> > +++ arch/armv7/armv7/armv7_machdep.c 4 Oct 2021 13:32:11 -0000
> > @@ -453,6 +453,12 @@ initarm(void *arg0, void *arg1, void *ar
> > len = fdt_node_property(node, "openbsd,uefi-mmap-desc-ver",
> > &prop);
> > if (len == sizeof(mmap_desc_ver))
> > mmap_desc_ver = bemtoh32((uint32_t *)prop);
> > +
> > + len = fdt_node_property(node, "openbsd,dma-constraint", &prop);
> > + if (len == sizeof(uint64_t[2])) {
> > + dma_constraint.ucr_low = bemtoh64((uint64_t *)prop);
> > + dma_constraint.ucr_high = bemtoh64((uint64_t *)prop +
> > 1);
> > + }
> > }
> >
> > process_kernel_args();
> > Index: arch/armv7/stand/efiboot/conf.c
> > ===================================================================
> > RCS file: src/sys/arch/armv7/stand/efiboot/conf.c,v
> > retrieving revision 1.31
> > diff -u -p -r1.31 conf.c
> > --- arch/armv7/stand/efiboot/conf.c 10 Jun 2021 22:17:58 -0000 1.31
> > +++ arch/armv7/stand/efiboot/conf.c 4 Oct 2021 13:32:11 -0000
> > @@ -42,7 +42,7 @@
> > #include "efidev.h"
> > #include "efipxe.h"
> >
> > -const char version[] = "1.18";
> > +const char version[] = "1.19";
> > int debug = 0;
> >
> > struct fs_ops file_system[] = {
> > Index: arch/armv7/stand/efiboot/efiboot.c
> > ===================================================================
> > RCS file: src/sys/arch/armv7/stand/efiboot/efiboot.c,v
> > retrieving revision 1.34
> > diff -u -p -r1.34 efiboot.c
> > --- arch/armv7/stand/efiboot/efiboot.c 7 Jun 2021 21:18:31 -0000
> > 1.34
> > +++ arch/armv7/stand/efiboot/efiboot.c 4 Oct 2021 13:32:11 -0000
> > @@ -435,6 +435,28 @@ efi_framebuffer(void)
> > sizeof(framebuffer_path));
> > }
> >
> > +uint64_t dma_constraint[2] = { 0, -1 };
> > +
> > +void
> > +efi_dma_constraint(void)
> > +{
> > + void *node;
> > +
> > + /* Raspberry Pi 4 is "special". */
> > + node = fdt_find_node("/");
> > + if (fdt_node_is_compatible(node, "brcm,bcm2711"))
> > + dma_constraint[1] = htobe64(0x3bffffff);
> > +
> > + /* Not all bus masters can access 0x40000-0x7ffff on Zynq-7000. */
Even range 0x0-0x3ffff has fine print on it, so I will change the above
comment to:
/* Not all bus masters can access 0x0-0x7ffff on Zynq-7000. */
> > + if (fdt_node_is_compatible(node, "xlnx,zynq-7000"))
> > + dma_constraint[0] = htobe64(0x00080000);
> > +
> > + /* Pass DMA constraint. */
> > + node = fdt_find_node("/chosen");
> > + fdt_node_add_property(node, "openbsd,dma-constraint",
> > + dma_constraint, sizeof(dma_constraint));
> > +}
> > +
> > void
> > efi_console(void)
> > {
> > @@ -515,6 +537,7 @@ efi_makebootargs(char *bootargs, int how
> >
> > efi_framebuffer();
> > efi_console();
> > + efi_dma_constraint();
> >
> > fdt_finalize();
> >
> >
> >
>
