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[23.128.96.18]) by mx.google.com with ESMTP id y13si8061447ejb.599.2020.05.24.09.14.12; Sun, 24 May 2020 09:14:34 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=GRgqbDTT; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387671AbgEXQM2 (ORCPT + 99 others); Sun, 24 May 2020 12:12:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:53092 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727899AbgEXQM2 (ORCPT ); Sun, 24 May 2020 12:12:28 -0400 Received: from archlinux (cpc149474-cmbg20-2-0-cust94.5-4.cable.virginm.net [82.4.196.95]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6FCFD20776; Sun, 24 May 2020 16:12:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590336746; bh=MDvWQIJHTHAoKsAitZGo0oA2UKmgx6b2YNAAIpEubio=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=GRgqbDTTw/YSjWOzZxwdoMCESdPizOXOj7/+zLwWWLqYxuuKLxDYJLSXoiYNPdMsQ zqnhSLuTq7iLuEioNJaoBZ2Bk7imo4NTJzPdXgWW34brPREnCTTc6miguoIUChA7hE 6M2011hYR/DWkRaqbMm8G+AqTl3BjwYn35ukqrx8= Date: Sun, 24 May 2020 17:12:21 +0100 From: Jonathan Cameron To: William Breathitt Gray Cc: 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 2/4] docs: counter: Update to reflect sysfs internalization Message-ID: <20200524171221.3ccb8c2f@archlinux> In-Reply-To: <2a8d7fe2e0ea435e19c89ba2aff15218c7b6eb91.1589654470.git.vilhelm.gray@gmail.com> References: <2a8d7fe2e0ea435e19c89ba2aff15218c7b6eb91.1589654470.git.vilhelm.gray@gmail.com> X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 16 May 2020 15:20:00 -0400 William Breathitt Gray wrote: > The Counter subsystem architecture and driver implementations have > changed in order to handle Counter sysfs interactions in a more > consistent way. This patch updates the Generic Counter interface > documentation to reflect the changes. > > Signed-off-by: William Breathitt Gray Looks good to me. Jonathan > --- > Documentation/driver-api/generic-counter.rst | 215 +++++++++++++------ > 1 file changed, 149 insertions(+), 66 deletions(-) > > diff --git a/Documentation/driver-api/generic-counter.rst b/Documentation/driver-api/generic-counter.rst > index e622f8f6e56a..8f85c30dea0b 100644 > --- a/Documentation/driver-api/generic-counter.rst > +++ b/Documentation/driver-api/generic-counter.rst > @@ -250,8 +250,8 @@ for defining a counter device. > .. kernel-doc:: drivers/counter/counter.c > :export: > > -Implementation > -============== > +Driver Implementation > +===================== > > To support a counter device, a driver must first allocate the available > Counter Signals via counter_signal structures. These Signals should > @@ -267,25 +267,58 @@ respective counter_count structure. These counter_count structures are > set to the counts array member of an allocated counter_device structure > before the Counter is registered to the system. > > -Driver callbacks should be provided to the counter_device structure via > -a constant counter_ops structure in order to communicate with the > -device: to read and write various Signals and Counts, and to set and get > -the "action mode" and "function mode" for various Synapses and Counts > -respectively. > +Driver callbacks must be provided to the counter_device structure in > +order to communicate with the device: to read and write various Signals > +and Counts, and to set and get the "action mode" and "function mode" for > +various Synapses and Counts respectively. > > A defined counter_device structure may be registered to the system by > passing it to the counter_register function, and unregistered by passing > it to the counter_unregister function. Similarly, the > -devm_counter_register and devm_counter_unregister functions may be used > -if device memory-managed registration is desired. > - > -Extension sysfs attributes can be created for auxiliary functionality > -and data by passing in defined counter_device_ext, counter_count_ext, > -and counter_signal_ext structures. In these cases, the > -counter_device_ext structure is used for global/miscellaneous exposure > -and configuration of the respective Counter device, while the > -counter_count_ext and counter_signal_ext structures allow for auxiliary > -exposure and configuration of a specific Count or Signal respectively. > +devm_counter_register function may be used if device memory-managed > +registration is desired. > + > +The struct counter_data structure is used to define counter extensions > +for Signals, Synapses, and Counts. > + > +The "type" member specifies the type of data (e.g. unsigned long, > +boolean, etc.) handled by this extension. The "read" and "write" members > +can then be set by the counter device driver with callbacks to handle > +that data. > + > +Convenience macros such as `COUNTER_DATA_COUNT_U64` are provided for use > +by driver authors. In particular, driver authors are expected to use > +the provided macros for standard Counter subsystem attributes in order > +to maintain a consistent interface for userspace. For example, a counter > +device driver may define several standard attributes like so:: > + > + struct counter_data count_ext[] = { > + COUNTER_DATA_DIRECTION(count_direction_read), > + COUNTER_DATA_ENABLE(count_enable_read, count_enable_write), > + COUNTER_DATA_CEILING(count_ceiling_read, count_ceiling_write), > + }; > + > +This makes it intuitive to see, add, and modify the attributes that are > +supported by this driver ("direction", "enable", and "ceiling") and to > +maintain this code without getting lost in a web of struct braces. > + > +Callbacks must match the function type expected for the respective > +component or extension. These function types are defined in the struct > +counter_data structure as the "`*_read`" and "`*_write`" union members. > + > +The corresponding callback prototypes for the extensions mentioned in > +the previous example above would be:: > + > + int count_direction_read(struct counter_device *counter, > + struct counter_count *count, u8 *direction); > + int count_enable_read(struct counter_device *counter, > + struct counter_count *count, u8 *enable); > + int count_enable_write(struct counter_device *counter, > + struct counter_count *count, u8 enable); > + int count_ceiling_read(struct counter_device *counter, > + struct counter_count *count, u64 *ceiling); > + int count_ceiling_write(struct counter_device *counter, > + struct counter_count *count, u64 ceiling); > > Determining the type of extension to create is a matter of scope. > > @@ -313,52 +346,102 @@ Determining the type of extension to create is a matter of scope. > chip overheated via a device extension called "error_overtemp": > /sys/bus/counter/devices/counterX/error_overtemp > > -Architecture > -============ > - > -When the Generic Counter interface counter module is loaded, the > -counter_init function is called which registers a bus_type named > -"counter" to the system. Subsequently, when the module is unloaded, the > -counter_exit function is called which unregisters the bus_type named > -"counter" from the system. > - > -Counter devices are registered to the system via the counter_register > -function, and later removed via the counter_unregister function. The > -counter_register function establishes a unique ID for the Counter > -device and creates a respective sysfs directory, where X is the > -mentioned unique ID: > - > - /sys/bus/counter/devices/counterX > - > -Sysfs attributes are created within the counterX directory to expose > -functionality, configurations, and data relating to the Counts, Signals, > -and Synapses of the Counter device, as well as options and information > -for the Counter device itself. > - > -Each Signal has a directory created to house its relevant sysfs > -attributes, where Y is the unique ID of the respective Signal: > - > - /sys/bus/counter/devices/counterX/signalY > - > -Similarly, each Count has a directory created to house its relevant > -sysfs attributes, where Y is the unique ID of the respective Count: > - > - /sys/bus/counter/devices/counterX/countY > - > -For a more detailed breakdown of the available Generic Counter interface > -sysfs attributes, please refer to the > -Documentation/ABI/testing/sysfs-bus-counter file. > - > -The Signals and Counts associated with the Counter device are registered > -to the system as well by the counter_register function. The > -signal_read/signal_write driver callbacks are associated with their > -respective Signal attributes, while the count_read/count_write and > -function_get/function_set driver callbacks are associated with their > -respective Count attributes; similarly, the same is true for the > -action_get/action_set driver callbacks and their respective Synapse > -attributes. If a driver callback is left undefined, then the respective > -read/write permission is left disabled for the relevant attributes. > - > -Similarly, extension sysfs attributes are created for the defined > -counter_device_ext, counter_count_ext, and counter_signal_ext > -structures that are passed in. > +Subsystem Architecture > +====================== > + > +Counter drivers pass and take data natively (i.e. `u8`, `u64`, `char *`, > +etc.) and the shared counter module handles the translation between the > +sysfs interface. This gurantees a standard userspace interface for all > +counter drivers, and helps generalize the Generic Counter driver ABI in > +order to support the Generic Counter chrdev interface without > +significant changes to the existing counter drivers. > + > +A high-level view of how a count value is passed down from a counter > +driver can be exemplified by the following:: > + > + Count data request: > + ~~~~~~~~~~~~~~~~~~~ > + ---------------------- > + / Counter device \ > + +----------------------+ > + | Count register: 0x28 | > + +----------------------+ > + | > + ----------------- > + / raw count data / > + ----------------- > + | > + V > + +----------------------------+ > + | Counter device driver |----------+ > + +----------------------------+ | > + | Processes data from device | ------------------- > + |----------------------------| / driver callbacks / > + | Type: unsigned long | ------------------- > + | Value: 42 | | > + +----------------------------+ | > + | | > + ---------------- | > + / unsigned long / | > + ---------------- | > + | | > + | V > + | +----------------------+ > + | | Counter core | > + | +----------------------+ > + | | Routes device driver | > + | | callbacks to the | > + | | userspace interfaces | > + | +----------------------+ > + | | > + | ------------------- > + | / driver callbacks / > + | ------------------- > + | | > + +-------+ | > + | | > + | +---------------+ > + | | > + V | > + +--------------------+ | > + | Counter sysfs |<-+ > + +--------------------+ > + | Translates to the | > + | standard Counter | > + | sysfs output | > + |--------------------| > + | Type: const char * | > + | Value: "42" | > + +--------------------+ > + | > + --------------- > + / const char * / > + --------------- > + | > + V > + +--------------------------------------------------+ > + | `/sys/bus/counter/devices/counterX/countY/count` | > + +--------------------------------------------------+ > + \ Count: "42" / > + -------------------------------------------------- > + > +There are three primary components involved: > + > +Counter device driver > +--------------------- > +Communicates with the hardware device to read/write data; e.g. counter > +drivers for quadrature encoders, timers, etc. > + > +Counter core > +------------ > +Registers the counter device driver to the system so that the respective > +callbacks are called during userspace interaction. > + > +Counter sysfs > +------------- > +Translates counter data to the standard Counter sysfs interface format > +and vice versa. > + > +Please refer to the `Documentation/ABI/testing/sysfs-bus-counter` file > +for a detailed breakdown of the available Generic Counter interface > +sysfs attributes.