From mboxrd@z Thu Jan 1 00:00:00 1970 From: Linus Walleij Subject: Re: [patch v6 0/3] JTAG driver introduction Date: Thu, 24 Aug 2017 23:07:29 +0200 Message-ID: References: <1503418256-5215-1-git-send-email-oleksandrs@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <1503418256-5215-1-git-send-email-oleksandrs-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Oleksandr Shamray Cc: Greg KH , Arnd Bergmann , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , OpenBMC Maillist , Joel Stanley , jiri-rHqAuBHg3fBzbRFIqnYvSA@public.gmane.org, Tobias Klauser , "linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , mec-WqBc5aa1uDFeoWH0uzbU5w@public.gmane.org, vadimp-45czdsxZ+A5DPfheJLI6IQ@public.gmane.org, system-sw-low-level-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, Rob Herring , openocd-devel-owner-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, "linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-api@vger.kernel.org On Tue, Aug 22, 2017 at 6:10 PM, Oleksandr Shamray 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 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html