Hello,

On 4 August 2015 at 19:59, R, Vignesh [off-list ref] wrote:

On 8/4/2015 9:21 PM, Mark Brown wrote:

quoted

On Mon, Aug 03, 2015 at 10:27:19AM +0530, Vignesh R wrote:

quoted

@use_mmap_mode: Some SPI controller chips are optimized for interacting
with serial flash memories. These chips have memory mapped interface,
through which entire serial flash memory slave can be read/written as if
though they are physical memories (like RAM). Using this interface,
flash can be accessed using memcpy() function and the spi controller
hardware will take care of communicating with serial flash over SPI.
Setting this flag will indicate the SPI controller driver that the
spi_message is from mtd layer to read from/write to flash. The SPI
master driver can then appropriately switch the controller to memory
mapped interface to read from/write to flash, based on this flag (See
drivers/spi/spi-ti-qspi.c for example).
NOTE: If the SPI controller chip lacks memory mapped interface, then the
driver will ignore this flag and use normal SPI protocol to read
from/write to flash. Communication with non-flash SPI devices is not
possible using the memory mapped interface.

I still can't tell from the above what this interface is supposed to do.
It sounds like the use of memory mapped mode is supposed to be
transparent to users, it should just affect how the controller interacts
with the hardware, but if that's the case why do we need to expose it to
users at all?  Shouldn't the driver just use memory mapped mode if it's
faster?

TI QSPI controller has two blocks:
1. SPI_CORE: This is generic(normal) spi mode. This can be used to
communicate with any SPI devices (serial flashes as well as non-flash
devices like touchscreen).
2. SFI_MM_IF(SPI memory mapped interface): The SFI_MM_IF block only
allows reading and writing to an SPI flash device only. Used to speed up
flash reads. It _cannot_ be used to communicate with non flash devices.
Now, the spi_message that ti-qspi receives in transfer_one() callback
can be from mtd device(in which case SFI_MM_IF can be used) or from any
other non flash SPI device (in which case SFI_MM_IF must not be used
instead SPI_CORE is to be used) but there is no way(is there?) to
distinguish where spi_message is from. Therefore I introduced flag
(use_mmap_mode) to struct spi_message. mtd driver will set flag to true,
this helps the ti-qspi driver to determine that the user is flash device
and thus can do read via SFI_MM_IF. If this flag is not set then the
user is assumed to be non flash SPI driver and will use SPI_CORE block
to communicate.

On the whole, I just need a way to determine that the user is a flash
device in order to switch to memory mapped interface.

Maybe it can be set on the SPI slave rather than each message.

Thanks

Michal