On Thu, Aug 24, 2017 at 2:07 PM, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > On Tue, Aug 22, 2017 at 6:10 PM, Oleksandr Shamray > <oleksandrs@xxxxxxxxxxxx> wrote: > >> SoC which are not equipped with JTAG master interface, can be built >> on top of JTAG core driver infrastructure, by applying bit-banging of >> TDI, TDO, TCK and TMS pins within the hardware specific driver. > > I guess you mean it should then use GPIO lines for bit-banging? > > I was wondering about how some JTAG clients like openOCD does > this in some cases. > Many common uses of OpenOCD leverage USB devices, such as FTDI FT232R, that have a command queue for bitbanging operations. Managing these via libusb is ugly but platform-agnostic. > In my worst nightmare they export GPIO lines using > the horrid ABI in /sys/gpio/* > https://sourceforge.net/p/openocd/code/ci/v0.10.0/tree/src/jtag/drivers/sysfsgpio.c While that is certainly horrible (and slow), mapping in the GPIO registers via /dev/mem strikes me as worse: https://sourceforge.net/p/openocd/code/ci/v0.10.0/tree/src/jtag/drivers/bcm2835gpio.c > In best case they use the GPIO character device or even > libgpiod. > > But having a JTAG abstraction inside the kernel that can > grab a few lines for JTAG defined in a device tree, ACPI DSDT > or similar makes sense too, as it abstracts the hardware so the > JTAG client can then just open whatever /dev/jtag0 is on the machine > and go ahead without having to bother about what GPIO lines > are connected exactly where. > > Yours, > Linus Walleij -- 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
