[U-Boot] [PATCH v2] sunxi: Support booting from SPI flash

[Siarhei Siamashka]

Hi Simon,

On Thu, 9 Jun 2016 17:36:10 -0700
Simon Glass <sjg at chromium.org> wrote:

> Hi,
> 
> On 7 June 2016 at 05:28, Siarhei Siamashka <siarhei.siamashka at gmail.com> wrote:
> > Allwinner devices support SPI flash as one of the possible
> > bootable media type. The SPI flash chip needs to be connected
> > to SPI0 pins (port C) to make this work. More information is
> > available at:
> >
> >     https://linux-sunxi.org/Bootable_SPI_flash
> >
> > This patch adds the initial support for booting from SPI flash.
> > The existing SPI frameworks are not used in order to reduce the
> > SPL code size. Right now the SPL size grows by ~370 bytes when
> > CONFIG_SPL_SPI_SUNXI option is enabled.
> >
> > While there are no popular Allwinner devices with SPI flash at
> > the moment, testing can be done using a SPI flash module (it
> > can be bought for ~2$ on ebay) and jumper wires with the boards,
> > which expose relevant pins on the expansion header. The SPI flash
> > chips themselves are very cheap (some prices are even listed as
> > low as 4 cents) and should not cost much if somebody decides to
> > design a development board with an SPI flash chip soldered on
> > the PCB.
> >
> > Another nice feature of the SPI flash is that it can be safely
> > accessed in a device-independent way (since we know that the
> > boot ROM is already probing these pins during the boot time).
> > And if, for example, Olimex boards opted to use SPI flash instead
> > of EEPROM, then they would have been able to have U-Boot installed
> > in the SPI flash now and boot the rest of the system from the SATA
> > hard drive. Hopefully we may see new interesting Allwinner based
> > development boards in the future, now that the software support
> > for the SPI flash is in a better shape :-)
> >
> > Testing can be done by enabling the CONFIG_SPL_SPI_SUNXI option
> > in a board defconfig, then building U-Boot and finally flashing
> > the resulting u-boot-sunxi-with-spl.bin binary over USB OTG with
> > a help of the sunxi-fel tool:
> >
> >    sunxi-fel spiflash-write 0 u-boot-sunxi-with-spl.bin
> >
> > The device needs to be switched into FEL (USB recovery) mode first.
> > The most suitable boards for testing are Orange Pi PC and Pine64.
> > Because these boards are cheap, have no built-in NAND/eMMC and
> > expose SPI0 pins on the Raspberry Pi compatible expansion header.
> > The A13-OLinuXino-Micro board also can be used.
> >
> > Signed-off-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>
> > ---
> >
> > Changes in v2:
> >  - Add Kconfig option (CONFIG_SPL_SPI_SUNXI) and move the SPI flash
> >    support code into a separate source file
> >  - Use CONFIG_SYS_SPI_U_BOOT_OFFS instead of the hardcoded constant
> >  - Deinitialize the SPI controller and undo pin muxing after the job
> >    is done
> >  - Size reduction of the SPI transfer function
> >  - Add delay after each SPI transfer to ensure that the chip select
> >    deassert timing requirements (tSHSL) are always satisfied
> >  - More comments in the code
> >
> >
> >  arch/arm/include/asm/arch-sunxi/gpio.h |   3 +
> >  arch/arm/mach-sunxi/board.c            |   5 +
> >  common/spl/spl.c                       |   4 +-
> >  drivers/mtd/spi/Kconfig                |  12 ++
> >  drivers/mtd/spi/Makefile               |   1 +
> >  drivers/mtd/spi/sunxi_spi_spl.c        | 283 +++++++++++++++++++++++++++++++++
> >  include/configs/sunxi-common.h         |   5 +
> >  7 files changed, 311 insertions(+), 2 deletions(-)
> >  create mode 100644 drivers/mtd/spi/sunxi_spi_spl.c  
> 
> Shouldn't this be a normal SPI driver? Then you could put this in
> common/spl/spl_spi.c.

This source file contains both a sunxi SPI controller support and a
basic SPI flash read functionality glued together for size reduction
purposes.

We are interested in implementing the "spl_spi_load_image()" function,
because this is what gets called when handling the BOOT_DEVICE_SPI
case.

The "drivers/mtd/spi" directory contains the "spi_spl_load.c" file,
which implements this particular function with the help of the generic
SPI flash support code from "spi_flash.c" and the generic SPI bus
support provided by the code from the "drivers/spi" directory.

What I'm doing in this patch is an implementation of a size reduced
sunxi-specific replacement for "spi_spl_load.c". But in U-Boot proper
(where the code size is not a problem anymore) we will need a real
sunxi SPI driver.

-- 
Regards,
Sierž