[PATCH 1/2] common: fdt: Add a function for reserving memory without kernel linear mapping

Michael Nazzareno Trimarchi
2020-02-29T10:44:39Z

Hi

On Wed, Feb 26, 2020 at 4:33 PM Simon Glass <sjg@chromium.org> wrote:
>
> Hi Michael,
>
> On Mon, 24 Feb 2020 at 22:10, Michael Trimarchi
> <michael@amarulasolutions.com> wrote:
> >
> > The intent is to reserve memory _and_ prevent it from being included
> > in the kernel's linear map. For thos reason it is also necessary to include the
> > 'no-map' property for this reserved-mem node.
> >
> > From Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt:
> >
> > no-map (optional) - empty property
> > - Indicates the operating system must not create a virtual mapping
> > of the region as part of its standard mapping of system memory,
> > nor permit speculative access to it under any circumstances other
> > than under the control of the device driver using the region.
> >
> > Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
> > ---
> > Changes: RFC->v1
> > - Add a better commit message
> > ---
> > common/fdt_support.c | 40 ++++++++++++++++++++++++++++++++++++++++
> > include/fdt_support.h | 11 +++++++++++
> > 2 files changed, 51 insertions(+)
> >
> > diff --git a/common/fdt_support.c b/common/fdt_support.c
> > index 02cf5c6241..a3662f4358 100644
> > --- a/common/fdt_support.c
> > +++ b/common/fdt_support.c
> > @@ -410,6 +410,46 @@ static int fdt_pack_reg(const void *fdt, void *buf, u64 *address, u64 *size,
> > return p - (char *)buf;
> > }
> >
> > +int fdt_fixup_reserved_memory(void *blob, const char *area, u64 start[], u64 size[])
> > +{
> > + int offs, len;
> > + const char *subpath;
> > + const char *path = "/reserved-memory";
> > + fdt32_t address_cells = cpu_to_fdt32(fdt_address_cells(blob, 0));
> > + fdt32_t size_cells = cpu_to_fdt32(fdt_size_cells(blob, 0));
> > + u8 temp[16]; /* Up to 64-bit address + 64-bit size */
> > +
> > + offs = fdt_path_offset(blob, path);
> > + if (offs < 0) {
> > + debug("Node %s not found\n", path);
> > + path = "/";
> > + subpath = "reserved-memory";
> > + offs = fdt_path_offset(blob, path);
>
> Error check
>

Ok

> > + offs = fdt_add_subnode(blob, offs, subpath);
> > + if (offs < 0) {
> > + printf("Could not create %s%s node.\n", path, subpath);
> > + return -1;
> > + }
> > + path = "/reserved-memory";
> > + offs = fdt_path_offset(blob, path);
> > +
> > + fdt_setprop(blob, offs, "#address-cells", &address_cells, sizeof(address_cells));
> > + fdt_setprop(blob, offs, "#size-cells", &size_cells, sizeof(size_cells));
> > + fdt_setprop(blob, offs, "ranges", NULL, 0);
>
> Need error-checking on these three
>

ok

> > + }
> > +
> > + offs = fdt_add_subnode(blob, offs, area ? : "private");
>
> Is this in a binding file somewhere?
>

The reserved memory is needed to avoid the linux kernel to use it and
to get a persistent framebuffer. On some SoC I have implemented the
reuse on the memory on their graphics driver. I need to check how this
is
documented in Linux. The name of the reserved memory it's not mandatory.

> > + if (offs < 0) {
> > + printf("Could not create %s%s node.\n", path, subpath);
> > + return -1;
>
> return offs
>

ok

> > + }
> > +
> > + fdt_setprop(blob, offs, "no-map", NULL, 0);
>
> and this?
>
ok

> Also needs error check
>
> > + len = fdt_pack_reg(blob, temp, start, size, 1);
> > + fdt_setprop(blob, offs, "reg", temp, len);
>
> blank line before return
>

done

> > + return 0;
> > +}
> > +
> > #if CONFIG_NR_DRAM_BANKS > 4
> > #define MEMORY_BANKS_MAX CONFIG_NR_DRAM_BANKS
> > #else
> > diff --git a/include/fdt_support.h b/include/fdt_support.h
> > index ba14acd7f6..7c8a280f53 100644
> > --- a/include/fdt_support.h
> > +++ b/include/fdt_support.h
> > @@ -93,6 +93,17 @@ void do_fixup_by_compat_u32(void *fdt, const char *compat,
> > */
> > int fdt_fixup_memory(void *blob, u64 start, u64 size);
> >
> > +/**
> > + * Setup the memory reserved node in the DT. Creates one if none was existing before.
> > + *
> > + * @param blob FDT blob to update
> > + * @param area Reserved area name
> > + * @param start Begin of DRAM mapping in physical memory
> > + * @param size Size of the single memory bank
> > + * @return 0 if ok, or -1 or -FDT_ERR_... on error
>
> Really we should return an FDT_ERR always. -1 is not a good idea and
> in fact is an FDT_ERR
>

Now with the change FDT_ERR only is returned.

> > + */
> > +int fdt_fixup_reserved_memory(void *blob, const char *area, u64 start[], u64 size[]);
> > +
> > /**
> > * Fill the DT memory node with multiple memory banks.
> > * Creates the node if none was existing before.
> > --
> > 2.17.1
> >
>
> Regards,
> Simon

I will post a new one

Michael