On 5 August 2015 at 13:50, Mark Brown <broo...@kernel.org> wrote: > On Tue, Aug 04, 2015 at 11:29:52PM +0530, R, Vignesh wrote: >> On 8/4/2015 9:21 PM, Mark Brown wrote: >> > On Mon, Aug 03, 2015 at 10:27:19AM +0530, Vignesh R wrote: > >> > 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? > >> 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. > > So if you're trying to do this you need to document it adequately so > that other people can understand what it is supposed to do and how to > use and implement it. People can't really tell how the interface is > supposed to work based on what was in the patch and the above isn't > really helping. For example, how does this change or restrict what the > contents of the spi_message are? > >> 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. > > As far as I can tell you want to set a per spi_message flag saying that > the message is a flash read command? If that's what this is trying to > do then why do you need to set the flag at all? If the message is in a > clearly defined format and it's more efficient to use this mmap mode > then surely the driver can just recognise that the format is approprate > and switch into mmap mode without being explicitly told - I'm not clear > what the flag adds here.
ehm, the read command is just one byte. I don't think sending 03 or other random byte as the first byte of a SPI transfer can be used as reliable detection that we are talking to a SPI flash memory. Thanks Michal -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
