Hi Simon,
On Thu, 9 Jun 2016 17:36:10 -0700 Simon Glass sjg@chromium.org wrote:
Hi,
On 7 June 2016 at 05:28, Siarhei Siamashka siarhei.siamashka@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_flashThis 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@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.