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Received: from [2600:1700:4830:165f::19e] (port=50504) by vern.gendns.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1kSpKL-0000An-70; Wed, 14 Oct 2020 18:32:57 -0400 Subject: Re: [PATCH v5 3/5] counter: Add character device interface To: William Breathitt Gray Cc: jic23@kernel.org, kamel.bouhara@bootlin.com, gwendal@chromium.org, alexandre.belloni@bootlin.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 References: <00be1fccc672c5207f3b04fe4cc09c29e22641f4.1601170670.git.vilhelm.gray@gmail.com> <67a0290e-731b-822a-5113-30b56bde6c88@lechnology.com> <20201014190526.GA13439@shinobu> From: David Lechner Message-ID: Date: Wed, 14 Oct 2020 17:32:55 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201014190526.GA13439@shinobu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - vern.gendns.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - lechnology.com X-Get-Message-Sender-Via: vern.gendns.com: authenticated_id: davidmain+lechnology.com/only user confirmed/virtual account not confirmed X-Authenticated-Sender: vern.gendns.com: davidmain@lechnology.com X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org On 10/14/20 2:05 PM, William Breathitt Gray wrote: > On Wed, Oct 14, 2020 at 12:43:08PM -0500, David Lechner wrote: >> On 9/26/20 9:18 PM, William Breathitt Gray wrote: >>> diff --git a/drivers/counter/counter-chrdev.c b/drivers/counter/counter-chrdev.c >>> new file mode 100644 >>> index 000000000000..2be3846e4105 >>> --- /dev/null >>> +++ b/drivers/counter/counter-chrdev.c >> >> >>> +/** >>> + * counter_push_event - queue event for userspace reading >>> + * @counter: pointer to Counter structure >>> + * @event: triggered event >>> + * @channel: event channel >>> + * >>> + * Note: If no one is watching for the respective event, it is silently >>> + * discarded. >>> + * >>> + * RETURNS: >>> + * 0 on success, negative error number on failure. >>> + */ >>> +int counter_push_event(struct counter_device *const counter, const u8 event, >>> + const u8 channel) >>> +{ >>> + struct counter_event ev = {0}; >>> + unsigned int copied = 0; >>> + unsigned long flags; >>> + struct counter_event_node *event_node; >>> + struct counter_comp_node *comp_node; >>> + int err; >>> + >>> + ev.timestamp = ktime_get_ns(); >>> + ev.watch.event = event; >>> + ev.watch.channel = channel; >>> + >>> + raw_spin_lock_irqsave(&counter->events_lock, flags); >>> + >>> + /* Search for event in the list */ >>> + list_for_each_entry(event_node, &counter->events_list, l) >>> + if (event_node->event == event && >>> + event_node->channel == channel) >>> + break; >>> + >>> + /* If event is not in the list */ >>> + if (&event_node->l == &counter->events_list) >>> + goto exit_early; >>> + >>> + /* Read and queue relevant comp for userspace */ >>> + list_for_each_entry(comp_node, &event_node->comp_list, l) { >>> + err = counter_get_data(counter, comp_node, &ev.value_u8); >> >> Currently all counter devices are memory mapped devices so calling >> counter_get_data() here with interrupts disabled is probably OK, but >> if any counter drivers are added that use I2C/SPI/etc. that will take >> a long time to read, it would cause problems leaving interrupts >> disabled here. >> >> Brainstorming: Would it make sense to separate the event from the >> component value being read? As I mentioned in one of my previous >> reviews, I think there are some cases where we would just want to >> know when an event happened and not read any additional data anyway. >> In the case of a slow communication bus, this would also let us >> queue the event in the kfifo and notify poll right away and then >> defer the reads in a workqueue for later. > > I don't see any problems with reporting just an event without any > component value attached (e.g. userspace could handle the component > reads via sysfs at a later point). We would just need a way to inform > userspace that the struct counter_component in the struct counter_watch > returned should be ignored. > > Perhaps we can add an additional member to struct counter_watch > indicating whether it's an empty watch; or alternatively, add a new > component scope define to differentiate between an actual component and > an empty one (e.g. COUNTER_SCOPE_EVENT). What do you think? > > William Breathitt Gray > I made the same suggestion in one of my other replies - except I called it COUNTER_SCOPE_NONE.