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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=no 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 DFED2C28CBC for ; Sun, 3 May 2020 14:13:27 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B366E2084D for ; Sun, 3 May 2020 14:13:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="uGysLx24"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Mom6aQXe" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B366E2084D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=3GL7+csgOBxD3TNUQ5ae694XNL30B+cIcBv/KyGh6Qg=; b=uGysLx24d8rgXs 1Vr+J/s0Qn0TmNDhSGsNsKkt8t5W6LuvKCv9VtJUVwiCyuCJKpDy+2pAeGf1eLUcFc47Veor8Au0c 7bL7lZrB9f3oGOZ/cJgKwTJfGkIugaS/oAbB9Lnnty4NxcAbSd42rnEujXI4VLbFr4jK2y9VpfS7L px7Pu+G6kJCwfvmYPqHvAkVuLrqpt2lUDLTzjJuKrz3L48+4yYVYZlSJ4Pt+yWyh2e44L2QP9abVO tM9HIVr2GUe7+158UwMrR96ngCT3igqNUJzIh4V153uJNikKM/Gbl1Go36ANozo8nvOa/TQY7BmWq Ey33C15OUpH7rywom60A==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVFN0-00010i-U6; Sun, 03 May 2020 14:13:26 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVFMw-0000zF-Np for linux-arm-kernel@lists.infradead.org; Sun, 03 May 2020 14:13:24 +0000 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 BFB512075B; Sun, 3 May 2020 14:13:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588515200; bh=VwFDi18uItpdaTttUtjRkKgBhmoR+CTBkU21YkTrWEQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Mom6aQXebEJMjo6moLHFErcGMYoEWb9EKBGiehFK98UmKFn71rYa0akF8nSXe1bwt 7zPAubNRfR9ZC2FAgv8CDsXwW8yKsRl8FMqoByL3BfrzYkLvCbj5ZtV6kcsGwmERPt cD+qW8PTdMcvcQsm8gS9uQlo6o5gFbLo9uOxJzW0= Date: Sun, 3 May 2020 15:13:14 +0100 From: Jonathan Cameron To: William Breathitt Gray Subject: Re: [PATCH 0/4] Introduce the Counter character device interface Message-ID: <20200503151314.2ac1fc2e@archlinux> In-Reply-To: References: X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200503_071322_821782_42447436 X-CRM114-Status: GOOD ( 36.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kamel.bouhara@bootlin.com, gwendal@chromium.org, david@lechnology.com, felipe.balbi@linux.intel.com, linux-iio@vger.kernel.org, syednwaris@gmail.com, alexandre.belloni@bootlin.com, linux-kernel@vger.kernel.org, mcoquelin.stm32@gmail.com, patrick.havelange@essensium.com, fabrice.gasnier@st.com, fabien.lahoudere@collabora.com, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, alexandre.torgue@st.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, 29 Apr 2020 14:11:34 -0400 William Breathitt Gray wrote: > Over the past couple years we have noticed some shortcomings with the > Counter sysfs interface. Although useful in the majority of situations, > there are certain use-cases where interacting through sysfs attributes > can become cumbersome and inefficient. A desire to support more advanced > functionality such as timestamps, multi-axis positioning tables, and > other such latency-sensitive applications, has motivated a reevaluation > of the Counter subsystem. I believe a character device interface will be > helpful for this more niche area of counter device use. > > To quell any concerns from the offset: this patchset makes no changes to > the existing Counter sysfs userspace interface -- existing userspace > applications will continue to work with no modifications necessary. I > request that driver maintainers please test their applications to verify > that this is true, and report any discrepancies if they arise. > > However, this patchset does contain a major reimplementation of the > Counter subsystem core and driver API. A reimplementation was necessary > in order to separate the sysfs code from the counter device drivers and > internalize it as a dedicated component of the core Counter subsystem > module. A minor benefit from all of this is that the sysfs interface is > now ensured a certain amount of consistency because the translation is > performed outside of individual counter device drivers. > > Essentially, the reimplementation has enabled counter device drivers to > pass and handle data as native C datatypes now rather than the sysfs > strings from before. A high-level view of how a count value is passed > down from a counter device driver can be exemplified by the following: > > ---------------------- > / 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 | V > +--------------------+ | +---------------------+ > | Counter sysfs |<-+->| Counter chrdev | > +--------------------+ +---------------------+ > | Translates to the | | Translates to the | > | standard Counter | | standard Counter | > | sysfs output | | character device | > |--------------------| |---------------------+ > | Type: const char * | | Type: unsigned long | > | Value: "42" | | Value: 42 | > +--------------------+ +---------------------+ > | | > --------------- ---------------- > / const char * / / unsigned long / > --------------- ---------------- > | | > | V > | +-----------+ > | | ioctl | > | +-----------+ > | \ Count: 42 / > | ----------- > | > V > +--------------------------------------------------+ > | `/sys/bus/counter/devices/counterX/countY/count` | > +--------------------------------------------------+ > \ Count: "42" / > -------------------------------------------------- > > I am aware that an in-kernel API can simplify the data transfer between > counter device drivers and the userspace interfaces, but I want to > postpone that development until after the new Counter character device > ioctl commands are solidified. A userspace ABI is effectively immutable > so I want to make sure we get that right before working on an in-kernel > API that is more flexible to change. However, when we do develop an > in-kernel API, it will likely be housed as part of the Counter core > component, through which the userspace interfaces will then communicate. > > Interaction with Counter character devices occurs via ioctl commands. > This allows userspace applications to access and set counter data using > native C datatypes rather than working through string translations. > > Regarding the organization of this patchset, I have combined the counter > device driver changes with the first patch because the changes must all > be taken together in order to avoid compilation errors. I can see how > this can end up making it difficult to review so many changes at once, > so alternatively I can separate out the counter device driver changes > into their own dedicated patches -- with the understanding that the > patches must all be taken together. > > In addition, I anticipate the Microchip TCB capture counter driver to > break with this patchset. I'm not sure how that driver will be picked > up yet so I have avoided adding it to this patchset right now. But the > changes to support that driver are simple to make so I can add them in a > later revision of this patchset. > > The following are some questions I have about this patchset: > > 1. Should enums be used to represent standard counter component states > (e.g. COUNTER_SIGNAL_LOW), or would these be better defined as int? > > These standard counter component states are defined in the > counter-types.h file and serve as constants used by counter device > drivers and Counter subsystem components in order to ensure a > consistent interface. > > My concern is whether enum constants will cause problems when passed > to userspace via the Counter character device ioctl calls. Along the > same lines is whether the C bool datatype is safe to pass as well, > given that it is a more modern C datatype. For enums, I'd pass them as integers. Bool is probably fine either way. > > 2. Should device driver callbacks return int or long? I sometimes see > error values returned as long (e.g. PTR_ERR(), the file_operations > structure's ioctl callbacks, etc.); when is it necessary to return > long as opposed to int? In my view it doesn't really matter that much. For PTR_ERR it has to be a long because a long is always the same length as a pointer, but an int 'might' not be. However PTR_ERR returns a value that always fits in an integer anyway. https://www.oreilly.com/library/view/linux-device-drivers/0596005903/ch11.html Coding style in linux mostly use int for return values that might indicate an error. > > 3. I only implemented the unlocked_ioctl callback. Should I implement a > compat_ioctl callback as well? Depends if you need to deal with the 32bit userspace on 64 bit kernel corner cases. Looks like you only pass a pointer, in which case I think you can just use the ioctl_compat_ptr callback to handle it for you. > > 4. How much space should allot for name strings? Name strings hold the > names of components (ideally as they appear on datasheets), so I've > arbitrarily chosen a size of 32 for the character device interface. > > 5. Should the owning component of an extension be determined by the > device driver or Counter subsystem? > > A lot of the complexity in the counters-function-types.h file and the > sysfs-callbacks.c file is due to the function pointer casts required > in order to support three different ownership scenarios: the owning > component is the device, the owning component is a Count, the owning > component is a Signal. > > Because the Counter subsystem doesn't not know which scenario is > valid, it must manually check and provide for all three ownership > cases. On the other hand, device drivers do know exactly which case > applies because they are the ones providing the callbacks. > > The complexity in the Counter subsystem code can be eliminated if the > owning component is simply passed down to the callbacks as a void > pointer. The device drivers will then be responsible for casting to > the appropriate component type, but this should in theory not be a > problem since the device driver assigned the callback to the owning > component in the first place. > > William Breathitt Gray (4): > counter: Internalize sysfs interface code > docs: counter: Update to reflect sysfs internalization > counter: Add character device interface > docs: counter: Document character device interface > > Documentation/driver-api/generic-counter.rst | 259 ++- > .../userspace-api/ioctl/ioctl-number.rst | 1 + > MAINTAINERS | 3 +- > drivers/counter/104-quad-8.c | 437 +++-- > drivers/counter/Makefile | 2 + > drivers/counter/counter-chrdev.c | 1134 +++++++++++++ > drivers/counter/counter-chrdev.h | 16 + > drivers/counter/counter-core.c | 220 +++ > drivers/counter/counter-function-types.h | 81 + > drivers/counter/counter-strings.h | 46 + > drivers/counter/counter-sysfs-callbacks.c | 566 +++++++ > drivers/counter/counter-sysfs-callbacks.h | 28 + > drivers/counter/counter-sysfs.c | 524 ++++++ > drivers/counter/counter-sysfs.h | 14 + > drivers/counter/counter.c | 1496 ----------------- > drivers/counter/ftm-quaddec.c | 46 +- > drivers/counter/stm32-lptimer-cnt.c | 159 +- > drivers/counter/stm32-timer-cnt.c | 132 +- > drivers/counter/ti-eqep.c | 170 +- > include/linux/counter.h | 547 +++--- > include/linux/counter_enum.h | 45 - > include/uapi/linux/counter-types.h | 67 + > include/uapi/linux/counter.h | 313 ++++ > 23 files changed, 3816 insertions(+), 2490 deletions(-) > create mode 100644 drivers/counter/counter-chrdev.c > create mode 100644 drivers/counter/counter-chrdev.h > create mode 100644 drivers/counter/counter-core.c > create mode 100644 drivers/counter/counter-function-types.h > create mode 100644 drivers/counter/counter-strings.h > create mode 100644 drivers/counter/counter-sysfs-callbacks.c > create mode 100644 drivers/counter/counter-sysfs-callbacks.h > create mode 100644 drivers/counter/counter-sysfs.c > create mode 100644 drivers/counter/counter-sysfs.h > delete mode 100644 drivers/counter/counter.c > delete mode 100644 include/linux/counter_enum.h > create mode 100644 include/uapi/linux/counter-types.h > create mode 100644 include/uapi/linux/counter.h > > > base-commit: 00edef1ac058b3c754d29bcfd35ea998d9e7a339 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel