From: Rick Altherr <raltherr-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
To: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Oleksandr Shamray
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<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [patch v6 0/3] JTAG driver introduction
Date: Thu, 24 Aug 2017 14:37:06 -0700 [thread overview]
Message-ID: <CAPLgG==Jj=Ys=SvhOCspSfunbWnuqPySvW9RfuqE8HYnG4C=ZQ@mail.gmail.com> (raw)
In-Reply-To: <CACRpkdZePXyo8Q36mBH7OnJU3E=yWPWSGkGUOH=zJFMjM=Yrhw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Thu, Aug 24, 2017 at 2:07 PM, Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
> On Tue, Aug 22, 2017 at 6:10 PM, Oleksandr Shamray
> <oleksandrs-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> 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
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next prev parent reply other threads:[~2017-08-24 21:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-22 16:10 [patch v6 0/3] JTAG driver introduction Oleksandr Shamray
2017-08-22 16:10 ` [patch v6 2/3] drivers: jtag: Add Aspeed SoC 24xx and 25xx families JTAG master driver Oleksandr Shamray
2017-08-22 16:10 ` [patch v6 3/3] Doccumentation: jtag: Add bindings for " Oleksandr Shamray
2017-08-28 8:36 ` Tobias Klauser
[not found] ` <1503418256-5215-1-git-send-email-oleksandrs-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2017-08-22 16:10 ` [patch v6 1/3] drivers: jtag: Add JTAG core driver Oleksandr Shamray
2017-08-24 21:07 ` [patch v6 0/3] JTAG driver introduction Linus Walleij
[not found] ` <CACRpkdZePXyo8Q36mBH7OnJU3E=yWPWSGkGUOH=zJFMjM=Yrhw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-24 21:37 ` Rick Altherr [this message]
2017-08-25 8:32 ` Linus Walleij
2017-08-25 8:50 ` Stuart Longland
[not found] ` <593cd0d3-8e06-0992-c155-1322014c0477-3e+Fe6x+DsgJbe36r25VNhCuuivNXqWP@public.gmane.org>
2017-08-25 16:53 ` Rick Altherr
2017-08-27 22:25 ` Linus Walleij
[not found] ` <CACRpkdbozWaL0RXyZXjzxYK3JHiqYziSkTGSgGORdptX-rwR8A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-25 16:52 ` Rick Altherr
[not found] ` <CAPLgG=mv1p98e4Vzso1N-VU=1MSotkTmnF+DcDTXPcd3q-n8HA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-27 22:30 ` Linus Walleij
[not found] ` <CACRpkdb75L5BrYN+V-BMwzrRm8_Wtymr3d08eMWt43FiBpH5Qg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-08-28 2:55 ` Rick Altherr
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