Get spiflash driver working

[mithro]

Be able to read the SPI flash...

• https://www.kernel.org/doc/Documentation/spi/

• Documentation/devicetree/bindings/spi/spi-bus.txt

• Documentation/devicetree/bindings/spi/spi-gpio.txt

• Documentation/devicetree/bindings/mtd/m25p80.txt

• Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt

• QEMU Emulation - https://github.com/timvideos/qemu-litex/issues/4

[mithro]

The following device tree was needed to get the spiflash bitbanging working;

    spiflash_bitbang_out: gpio-controller@e0005000 {
        compatible = "basic-mmio-gpio", "wd,mbl-gpio";
        reg = <0xe0005000 0x4>;
        #gpio-cells = <2>;
        gpio-controller;
        reg-names = "dat";
        big-endian;
    };
    spiflash_bitbang_in: gpio-controller@e0005004 {
        compatible = "basic-mmio-gpio", "wd,mbl-gpio";
        reg = <0xe0005004 0x4>;
        #gpio-cells = <2>;
        gpio-controller;
        reg-names = "dat";
        no-output;
        big-endian;
    };

        spi {
                compatible = "spi-gpio";
                #address-cells = <0x1>;
                ranges;

                gpio-mosi = <&spiflash_bitbang_out 0 0>;    // 0x01 on reg0
                gpio-sck =  <&spiflash_bitbang_out 1 0>;    // 0x02 on reg0
                cs-gpios =  <&spiflash_bitbang_out 2 0>;    // 0x03 on reg0
                gpio-miso =     <&spiflash_bitbang_in  0 0>;    // 0x01 on reg1
                num-chipselects = <1>;

                /* clients */
        m25p16@0 {
            #address-cells = <1>;
            #size-cells = <1>;
            compatible = "spansion,m25p16", "jedec,spi-nor";
            spi-max-frequency = <40000000>;
            reg = <0>;
            //m25p,fast-read;

            // Values in the partition table should be relative to the
            // flash start address...
            partitions {
                compatible = "fixed-partitions";
                #address-cells = <1>;
                #size-cells = <1>;

                /* FPGA gateware */
                partition@0 {
                    label = "gateware";
                    reg = <0x0000000 0x80000>;
                    read-only;
                };

                /* MiSoC / LiteX BIOS */
                partition@80000 {
                    label = "bios";
                    reg = <0x00080000 0x8000>;
                    read-only;
                };

                /* HDMI2USB Firmware (or Linux Kernel?) */
                partition@88000 {
                    label = "firmware";
                    reg = <0x00088000 0x178000>;
                    read-only;
                };
            };
        };
        };
    /************************************************************************/

You then get the following dmesg output;

m25p80 spi32766.0: m25p16 (2048 Kbytes)
3 ofpart partitions found on MTD device spi32766.0
Creating 3 MTD partitions on "spi32766.0":
0x000000000000-0x000000080000 : "gateware"
0x000000080000-0x000000088000 : "bios"
0x000000088000-0x000000200000 : "firmware"
spi_gpio spi: registered child spi32766.0