Re: [patch v6 0/3] JTAG driver introduction

[Linus Walleij]

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.

In my worst nightmare they export GPIO lines using
the horrid ABI in /sys/gpio/*

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