Hi Grant, > <phil.edwor...@renesas.com> wrote: > > The driver attempts to read the received data immediately after > > writing to the transmit buffer. If no data is available, the driver > > currently waits 20ms until trying again. Since the hardware needs > > to shift out the transmitted data, the first poll always fails, > > leading to 20ms delay between bytes. > > > > This patch waits for the time it takes to transmit a byte before > > reading the received data. > > > > Signed-off-by: Phil Edworthy <phil.edwor...@renesas.com> > > --- > > v2: > > Instead of replacing msleep(20) with udelay(1), this version now > > calculates the time it takes to shift out a byte, and uses udelay or > > ndelay for this time. After this it falls back to polling every 20ms > > using msleep. The delay has an empirical element based on testing at > > different speeds. <snip>
> This is still just busywaiting. Which means just burning CPU cycles > unconditionally even if it does finish early. > > Instead of doing nothing, it is actually a whole lot better to use a > small delay and check if there is stuff to do frequently than it is to > try and delay for the entire duration. Due to the way this driver is > architected, nothing else can use the CPU during the delay(). > > What would really be better is to load up the fifo and full as it will > go and then rely on IRQs to tell the driver when it becomes ready to > fill with more data. Ok, I see now. I'll look at using dma instead though, as that will be better in the long run. Thanks for your comments, Phil ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ spi-devel-general mailing list spi-devel-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spi-devel-general
