From: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
To: Stuart Longland
<stuartl-3e+Fe6x+DsgJbe36r25VNhCuuivNXqWP@public.gmane.org>
Cc: "Rick Altherr" <raltherr-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
"Oleksandr Shamray"
<oleksandrs-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>,
"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Jiří Pírko" <jiri-rHqAuBHg3fBzbRFIqnYvSA@public.gmane.org>,
"Arnd Bergmann" <arnd-r2nGTMty4D4@public.gmane.org>,
system-sw-low-level-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org,
"Greg KH"
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
"OpenBMC Maillist"
<openbmc-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
openocd-devel-owner-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
mec-WqBc5aa1uDFeoWH0uzbU5w@public.gmane.org,
"Rob Herring" <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
"linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"Tobias Klauser"
<tklauser-93Khv+1bN0NyDzI6CaY1VQ@public.gmane.org>,
"linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [patch v6 0/3] JTAG driver introduction
Date: Mon, 28 Aug 2017 00:25:14 +0200 [thread overview]
Message-ID: <CACRpkdbgbRgqi=sVs0Rk_qPLUFC6wwvcWKKdiDjfXHdUZ4EXjg@mail.gmail.com> (raw)
In-Reply-To: <593cd0d3-8e06-0992-c155-1322014c0477-3e+Fe6x+DsgJbe36r25VNhCuuivNXqWP@public.gmane.org>
On Fri, Aug 25, 2017 at 10:50 AM, Stuart Longland
<stuartl-3e+Fe6x+DsgJbe36r25VNhCuuivNXqWP@public.gmane.org> wrote:
> [Note: dropping vadimp-45czdsxZ+A5DPfheJLI6IQ@public.gmane.org as SMTP server complained about the
> DNS server returning NXDOMAIN. Apologies.]
> On 25/08/17 18:32, Linus Walleij wrote:
>> Gnah!
>> Whoever writes a slot-in replacement making the character device
>> take precendence wins lots of karma.
>
> What would such a replacement look like though?
Something that looks for /dev/gpiochipN and if it exists open the GPIOs
from there and make that take precedence over any /sys/gpio/*
poking.
> Some sort of system whereby you can read/write single-line commands as
> if talking to a GPIO expander over a UART?
I don't really understand the question. All GPIO expanders become
a gpiochip, and have their own character device in /dev.
> Would you access the GPIOs one by one, or would you perhaps map them
> into a bitmap (maybe arbitrarily, up to 64-bits wide) and perform masked
> operations on the bitmap?
The character device supports up to 64bits of simultaneous line
switches, but the in-kernel API can only handle 32bits
in a single register write.
> I'm no fan of the sysfs GPIO interface, but it beats poking around at
> registers behind the kernel's back.
Have a look at libgpiod and tools/gpio/* in the kernel.
Yours,
Linus Walleij
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next prev parent reply other threads:[~2017-08-27 22:25 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
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 [this message]
[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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