From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 953BCC433DF for ; Fri, 29 May 2020 13:26:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7D90E20721 for ; Fri, 29 May 2020 13:26:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726629AbgE2N0Q (ORCPT ); Fri, 29 May 2020 09:26:16 -0400 Received: from jabberwock.ucw.cz ([46.255.230.98]:45702 "EHLO jabberwock.ucw.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726792AbgE2N0P (ORCPT ); Fri, 29 May 2020 09:26:15 -0400 Received: by jabberwock.ucw.cz (Postfix, from userid 1017) id 904CF1C0389; Fri, 29 May 2020 15:26:14 +0200 (CEST) Date: Fri, 29 May 2020 15:26:04 +0200 From: Pavel Machek To: William Breathitt Gray Cc: jic23@kernel.org, kamel.bouhara@bootlin.com, gwendal@chromium.org, alexandre.belloni@bootlin.com, david@lechnology.com, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com, patrick.havelange@essensium.com, fabrice.gasnier@st.com, mcoquelin.stm32@gmail.com, alexandre.torgue@st.com Subject: Re: [PATCH v2 4/4] docs: counter: Document character device interface Message-ID: <20200529132604.GB1339@bug> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-iio-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On Sat 2020-05-16 15:20:02, William Breathitt Gray wrote: > This patch adds high-level documentation about the Counter subsystem > character device interface. > > Signed-off-by: William Breathitt Gray > --- > Documentation/driver-api/generic-counter.rst | 112 +++++++++++++------ > 1 file changed, 76 insertions(+), 36 deletions(-) > > diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst > index 8f85c30dea0b..58045b33b576 100644 > --- a/Documentation/driver-api/generic-counter.rst > +++ b/Documentation/driver-api/generic-counter.rst > + > +Counter chrdev > +-------------- > +Translates counter data to the standard Counter character device; data > +is transferred via standard character device read/write calls. > + > +Sysfs Interface > +=============== > + > +Several sysfs attributes are generated by the Generic Counter interface, > +and reside under the `/sys/bus/counter/devices/counterX` directory, > +where `X` is to the respective counter device id. Please see > +Documentation/ABI/testing/sysfs-bus-counter for detailed information on > +each Generic Counter interface sysfs attribute. > + > +Through these sysfs attributes, programs and scripts may interact with > +the Generic Counter paradigm Counts, Signals, and Synapses of respective > +counter devices. > + > +Counter Character Device > +======================== > + > +Counter character device nodes are created under the `/dev` directory as > +`counterX`, where `X` is the respective counter device id. Defines for > +the standard Counter data types are exposed via the userspace > +`include/uapi/linux/counter-types.h` file. > + > +The first 196095 bytes of the character device serve as a control > +selection area where control exposure of desired Counter components and > +extensions may be selected. Each byte serves as a boolean selection > +indicator for a respective Counter component or extension. The format of > +this area is as follows: > + > +* For each device extension, a byte is required. > +* For each Signal, a byte is reserved for the Signal component, and a > + byte is reserved for each Signal extension. > +* For each Count, a byte is reserved for the Count component, a byte is > + reserved for the count function, a byte is reserved for each Synapse > + action, and byte is reserved for each Count extension. > + > +The selected Counter components and extensions may then be interfaced > +after the first 196095 bytes via standard character device read/write > +operations. The number of bytes available for each component or > +extension is dependent on their respective data type: u8 will have 1 > +byte available, u64 will have 8 bytes available, strings will have 64 > +bytes available, etc. This looks like very, very strange interface, and not described in detail required to understand it. Could you take a look at input subsystem, /dev/input/event0? Perhaps it is directly usable, and if not something similar should probably be acceptable. Best regards, Pavel