Hello, On 4 August 2015 at 19:59, R, Vignesh <vigneshr@xxxxxx> wrote: > > > On 8/4/2015 9:21 PM, Mark Brown wrote: >> On Mon, Aug 03, 2015 at 10:27:19AM +0530, Vignesh R wrote: >> >>> @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 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
