[PATCH] doc: Move the generic memory-documentation to doc/
Tom Rini
trini at konsulko.com
Wed Sep 25 19:25:53 CEST 2024
On Wed, Sep 25, 2024 at 02:50:45PM +0200, Simon Glass wrote:
> Hi Heinrich,
>
> On Sun, 22 Sept 2024 at 11:02, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >
> > On 9/19/24 17:14, Simon Glass wrote:
> > > Move this section of the README into doc/ with some minor updates to
> > > mention SPL and user lower-case hex.
> > >
> > > Signed-off-by: Simon Glass <sjg at chromium.org>
> > > ---
> > >
> > > README | 45 ------------------------------------------
> > > doc/develop/index.rst | 1 +
> > > doc/develop/memory.rst | 45 ++++++++++++++++++++++++++++++++++++++++++
> > > 3 files changed, 46 insertions(+), 45 deletions(-)
> > > create mode 100644 doc/develop/memory.rst
> > >
> > > diff --git a/README b/README
> > > index 4be1e8c22a0..d73042406b6 100644
> > > --- a/README
> > > +++ b/README
> > > @@ -2516,51 +2516,6 @@ On RISC-V, the following registers are used:
> > >
> > > ==> U-Boot will use gp to hold a pointer to the global data
> > >
> > > -Memory Management:
> > > -------------------
> > > -
> > > -U-Boot runs in system state and uses physical addresses, i.e. the
> > > -MMU is not used either for address mapping nor for memory protection.
> > > -
> > > -The available memory is mapped to fixed addresses using the memory
> > > -controller. In this process, a contiguous block is formed for each
> > > -memory type (Flash, SDRAM, SRAM), even when it consists of several
> > > -physical memory banks.
> > > -
> > > -U-Boot is installed in the first 128 kB of the first Flash bank (on
> > > -TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
> > > -booting and sizing and initializing DRAM, the code relocates itself
> > > -to the upper end of DRAM. Immediately below the U-Boot code some
> > > -memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
> > > -configuration setting]. Below that, a structure with global Board
> > > -Info data is placed, followed by the stack (growing downward).
> > > -
> > > -Additionally, some exception handler code is copied to the low 8 kB
> > > -of DRAM (0x00000000 ... 0x00001FFF).
> > > -
> > > -So a typical memory configuration with 16 MB of DRAM could look like
> > > -this:
> > > -
> > > - 0x0000 0000 Exception Vector code
> > > - :
> > > - 0x0000 1FFF
> > > - 0x0000 2000 Free for Application Use
> > > - :
> > > - :
> > > -
> > > - :
> > > - :
> > > - 0x00FB FF20 Monitor Stack (Growing downward)
> > > - 0x00FB FFAC Board Info Data and permanent copy of global data
> > > - 0x00FC 0000 Malloc Arena
> > > - :
> > > - 0x00FD FFFF
> > > - 0x00FE 0000 RAM Copy of Monitor Code
> > > - ... eventually: LCD or video framebuffer
> > > - ... eventually: pRAM (Protected RAM - unchanged by reset)
> > > - 0x00FF FFFF [End of RAM]
> > > -
> > > -
> > > System Initialization:
> > > ----------------------
> > >
> > > diff --git a/doc/develop/index.rst b/doc/develop/index.rst
> > > index 0d0e60ab56c..cbea38d4323 100644
> > > --- a/doc/develop/index.rst
> > > +++ b/doc/develop/index.rst
> > > @@ -13,6 +13,7 @@ General
> > > codingstyle
> > > designprinciples
> > > docstyle
> > > + memory
> > > patman
> > > process
> > > release_cycle
> > > diff --git a/doc/develop/memory.rst b/doc/develop/memory.rst
> > > new file mode 100644
> > > index 00000000000..fa1ae5e97ed
> > > --- /dev/null
> > > +++ b/doc/develop/memory.rst
> > > @@ -0,0 +1,45 @@
> > > +.. SPDX-License-Identifier: GPL-2.0+:
> > > +
> > > +Memory Management
> > > +-----------------
> > > +
> > > +U-Boot runs in system state and uses physical addresses, i.e. the
> > > +MMU is not used either for address mapping nor for memory protection.
> >
> > Hello Simon,
> >
> > Thanks for getting the description moved.
> >
> > The text that you are copying dates back to 2004 when U-Boot was
> > focusing on the Power architecture. It needs some rework.
> >
> > On RISC-V there is a physical memory protection (PMP) which is typically
> > set up to guard against overwriting OpenSBI sitting at the lower end of RAM.
> >
> > There is some ongoing work to implement NX protection via the MMU for ARM.
> >
> > > +
> > > +The available memory is mapped to fixed addresses using the
> > > +memory-controller. In this process, a contiguous block is formed for each
> > > +memory type (Flash, SDRAM, SRAM), even when it consists of several
> > > +physical-memory banks.
> >
> > Can we simply say DRAM instead of SDRAM. We always refer to DRAM below.
> > Whether the RAM frequency is synchronous or not is irrelevant here.
> >
> > > +
> > > +U-Boot is installed in XIP flash memory, or may be loaded into a lower region of
> > > +RAM by a secondary program loader (SPL). After
> >
> > This does not describe U-Boot SPL as being a part of U-Boot.
> >
> > > +booting and sizing and initialising DRAM, the code relocates itself
> >
> > Initialization of DRAM can be done in code running before U-Boot.
> >
> > > +to the upper end of DRAM. Immediately below the U-Boot code some
> > > +memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN>
> > +configuration setting]. Below that, a structure with global Board-Info
> > > +data is placed, followed by the stack (growing downward).
> > > +
> > > +Additionally, some exception handler code may be copied to the low 8 kB
> > > +of DRAM (0x00000000 ... 0x00001fff).
> >
> > The exception handler code for RISC-V and ARMv8 is typically not located
> > at 0x0.
> >
> > On RISC-V stvec, the Supervisor Trap Vector Base Address Register,
> > defines where the exception vectors are located in S-Mode.
> >
> > On ARMv8 VBAR_EL2, the Vector Base Address Register (EL2), sets the
> > location of the EL2 vector base.
>
> I don't believe we need to get into the weeds on this description. It
> is just setting some guiding principles. Yes, every architecture is
> different, but people can see the general idea.
>
> Perhaps we should add details about each architecture at the end, i.e.
> provide a link to an arch-specific page which provides more
> information?
Perhaps we should start by moving this content out of the top-level
README and note at the start in the new document that the information is
outdated and needs to be updated.
--
Tom
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 659 bytes
Desc: not available
URL: <https://lists.denx.de/pipermail/u-boot/attachments/20240925/0878850e/attachment.sig>
More information about the U-Boot
mailing list