-----Original Message-----
From: geert.uytterhoeven at gmail.com [mailto:geert.uytterhoeven at gmail.com]
On Behalf Of Geert Uytterhoeven
Sent: Thursday, September 28, 2017 11:33 AM
To: Oleksandr Shamray <redacted>
Cc: Greg KH <gregkh@linuxfoundation.org>; Arnd Bergmann
[off-list ref]; linux-kernel at vger.kernel.org; linux-arm-
kernel at lists.infradead.org; devicetree at vger.kernel.org;
openbmc at lists.ozlabs.org; Joel Stanley [off-list ref]; Jiri Pirko
[off-list ref]; Tobias Klauser [off-list ref]; linux-
serial at vger.kernel.org; mec at shout.net; Vadim Pasternak
[off-list ref]; system-sw-low-level <system-sw-low-
level at mellanox.com>; Rob Herring [off-list ref]; openocd-devel-
owner at lists.sourceforge.net; linux-api at vger.kernel.org; David S. Miller
[off-list ref]; Mauro Carvalho Chehab [off-list ref];
linux-spi [off-list ref]; Mark Brown [off-list ref]
Subject: Re: [patch v9 0/4] JTAG driver introduction

Hi Oleksandr,

[My attention was drawn by
https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.net
%2FArticles%2F734440%2F&data=02%7C01%7Coleksandrs%40mellanox.com%7
C97b8ba88686a42daaace08d5064b92eb%7Ca652971c7d2e4d9ba6a4d149256f
461b%7C0%7C0%7C636421844026854216&sdata=TeHD4a3%2FBN6a5XG3Jizf5
pmsyJHJjzkEzkpnqsXC6S0%3D&reserved=0]
[CC linux-spi, which was never included, while linux-serial was]

On Thu, Sep 21, 2017 at 11:25 AM, Oleksandr Shamray
[off-list ref] wrote:

quoted

When a need raise up to use JTAG interface for system's devices
programming or CPU debugging, usually the user layer application
implements jtag protocol by bit-bang or using a proprietary connection
to vendor hardware.
This method can be slow and not generic.

[..]

quoted

Initial version provides the system calls set for:
- SIR (Scan Instruction Register, IEEE 1149.1 Data Register scan);
- SDR (Scan Data Register, IEEE 1149.1 Instruction Register scan);
- RUNTEST (Forces the IEEE 1149.1 bus to a run state for a specified
  number of clocks.

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.

Or by using an SPI master?

I think it depends on how flexible the SPI interface is. If you can set it to transfer 
from 1 to n bits at a time, and you control the TMS line in software, you should 
be able to use it. If the SPI interface can only transfer a multiple of 8 bits 
at a time, then in general it would not be suitable for JTAG.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-
m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds