RE: [patch v9 0/4] JTAG driver introduction

[Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>]

> -----Original Message-----
> From: geert.uytterhoeven@xxxxxxxxx [mailto:geert.uytterhoeven@xxxxxxxxx]
> On Behalf Of Geert Uytterhoeven
> Sent: Thursday, September 28, 2017 11:33 AM
> To: Oleksandr Shamray <oleksandrs@xxxxxxxxxxxx>
> Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>; Arnd Bergmann
> <arnd@xxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; devicetree@xxxxxxxxxxxxxxx;
> openbmc@xxxxxxxxxxxxxxxx; Joel Stanley <joel@xxxxxxxxx>; Jiri Pirko
> <jiri@xxxxxxxxxxx>; Tobias Klauser <tklauser@xxxxxxxxxx>; linux-
> serial@xxxxxxxxxxxxxxx; mec@xxxxxxxxx; Vadim Pasternak
> <vadimp@xxxxxxxxxxxx>; system-sw-low-level <system-sw-low-
> level@xxxxxxxxxxxx>; Rob Herring <robh+dt@xxxxxxxxxx>; openocd-devel-
> owner@xxxxxxxxxxxxxxxxxxxxx; linux-api@xxxxxxxxxxxxxxx; David S. Miller
> <davem@xxxxxxxxxxxxx>; Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>;
> linux-spi <linux-spi@xxxxxxxxxxxxxxx>; Mark Brown <broonie@xxxxxxxxxx>
> 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
> <oleksandrs@xxxxxxxxxxxx> wrote:
> > 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.
> >


[..]

> >
> > 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@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
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