README: qspi usecase and testing documentation.

Contains documentation and testing details for qspi flash
interface.

Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>

doc/SPI/README.ti_qspi_dra_test

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+-------------------------------------------------
+   Simple steps used to test the QSPI at U-Boot
+-------------------------------------------------
+
+For #1, build the patched U-Boot and load MLO/u-boot.img
+
+----------------------------------
+Boot from another medium like MMC
+----------------------------------
+
+U-Boot# mmc dev 0
+mmc0 is current device
+U-Boot# fatload mmc 0 0x82000000 MLO
+reading MLO
+55872 bytes read in 8 ms (6.7 MiB/s)
+U-Boot# fatload mmc 0 0x83000000 u-boot.img
+reading u-boot.img
+248600 bytes read in 19 ms (12.5 MiB/s)
+
+--------------------------------------------------
+Commands to erase/write u-boot/mlo to flash device
+--------------------------------------------------
+U-Boot# sf probe 0
+SF: Detected S25FL256S_64K with page size 256 Bytes, erase size 64 KiB, total 32 MiB, mapped at 5c000000
+SF: Warning - Only lower 16MiB accessible, Full access #define CONFIG_SPI_FLASH_BAR
+U-Boot# sf erase 0 0x10000
+SF: 65536 bytes @ 0x0 Erased: OK
+U-Boot# sf erase 0x20000 0x10000
+SF: 65536 bytes @ 0x20000 Erased: OK
+U-Boot# sf erase 0x30000 0x10000
+SF: 65536 bytes @ 0x30000 Erased: OK
+U-Boot# sf erase 0x40000 0x10000
+SF: 65536 bytes @ 0x40000 Erased: OK
+U-Boot# sf erase 0x50000 0x10000
+SF: 65536 bytes @ 0x50000 Erased: OK
+U-Boot# sf erase 0x60000 0x10000
+SF: 65536 bytes @ 0x60000 Erased: OK
+U-Boot# sf write 82000000 0 0x10000
+SF: 65536 bytes @ 0x0 Written: OK
+U-Boot# sf write 83000000 0x20000 0x60000
+SF: 393216 bytes @ 0x20000 Written: OK
+
+For #2, set sysboot to QSPI-1 boot mode(SYSBOOT[5:0] = 100110) and power
+on. ROM should find the GP header at offset 0 and load/execute SPL. SPL
+then detects that ROM was in QSPI-1 mode (boot code 10) and attempts to
+find a U-Boot image header at offset 0x20000 (set in the config file)
+and proceeds to load that image using the U-Boot image payload offset/size
+from the header. It will then start U-Boot.

doc/SPI/README.ti_qspi_flash

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+QSPI U-boot support
+------------------
+
+Host processor is connected to serial flash device via qpsi
+interface. QSPI is a kind of spi module that allows single,
+dual and quad read access to external spi devices. The module
+has a memory mapped interface which provide direct interface
+for accessing data form external spi devices.
+
+The one QSPI in the device is primarily intended for fast booting
+from Quad SPI flash devices.
+
+Usecase
+-------
+
+MLO/u-boot.img will be flashed from SD/MMC to the flash device
+using serial flash erase and write commands. Then, switch settings
+will be changed to qspi boot. Then, the ROM code will read MLO
+from the predefined location in the flash, where it was flashed and
+execute it after storing it in SDRAM. Then, the MLO will read
+u-boot.img from flash and execute it from SDRAM.
+
+SPI mode
+-------
+SPI mode uses mtd spi framework for transfer and reception of data.
+Can be used in:
+1. Normal mode: use single pin for transfers
+2. Dual Mode: use two pins for transfers.
+3. Quad mode: use four pin for transfer
+
+Memory mapped read mode
+-----------------------
+In this, SPI controller is configured using configuration port and then
+controler is switched to memory mapped port for data read.
+
+Driver
+------
+drivers/qspi/ti_qspi.c
+    - Newly created file which is responsible for configuring the
+	qspi controller and also for providing the low level api which
+	is responsible for transferring the datas from host controller
+	to flash device and vice versa.
+
+Testing
+-------
+A seperated file named README.dra_qspi_test has been created which gives all the
+details about the commands required to test qspi at u-boot level.