On April 18, 2015 2:09:26 PM GMT+02:00, Mark Brown <broo...@kernel.org> wrote: >On Mon, Apr 13, 2015 at 12:59:30PM +0200, Michael Grzeschik wrote: >> The current implementation of bitbang_txrx_be_cpha0 and >> bitbang_txrx_be_cpha1 always call setmosi. That runs into several >> unnecessary calls into the gpiolib when the level of the GPIO >actually >> has not to be changed. >> >> This patch changes the routines to remember the last GPIO level >> and only calls setmosi if an change has to be made. This >> way it improves the transfer throughput. > >Do you have any benchmarking or anything showing that this offers a >practical benefit? Generally a bitbanging system would be using memory >mapped GPIOs for the bus so we're talking about replacing a memory >access with some shifts and logic operations here and while I can >believe that something that runs in cache is going to be an overall win >over going out to a device it's not quite so clear cut as it could be.
IIRC we had a reduction of about 30% when programming an FPGA via SPI. But Michael can give you the exact numbers. Marc -- To unsubscribe from this list: send the line "unsubscribe linux-spi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
