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([2600:8803:e7e4:500:3be6:1187:fed4:378b]) by smtp.gmail.com with ESMTPSA id 5614622812f47-482ee0999f3sm5028432b6e.0.2026.05.18.08.16.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 May 2026 08:16:39 -0700 (PDT) Message-ID: <60d66897-41cc-4f3f-afd2-64e49f0bb55e@baylibre.com> Date: Mon, 18 May 2026 10:16:38 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 4/6] iio: adc: ad4691: add SPI offload support To: "Sabau, Radu bogdan" , Lars-Peter Clausen , "Hennerich, Michael" , Jonathan Cameron , "Sa, Nuno" , Andy Shevchenko , Rob Herring , Krzysztof Kozlowski , Conor Dooley , =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= , Liam Girdwood , Mark Brown , Linus Walleij , Bartosz Golaszewski , Philipp Zabel , Jonathan Corbet , Shuah Khan Cc: "linux-iio@vger.kernel.org" , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-pwm@vger.kernel.org" , "linux-gpio@vger.kernel.org" , "linux-doc@vger.kernel.org" References: <20260515-ad4692-multichannel-sar-adc-driver-v11-0-eab27d852ac2@analog.com> <20260515-ad4692-multichannel-sar-adc-driver-v11-4-eab27d852ac2@analog.com> <80f61c0b-1f36-4fee-9f76-b93f63b87abe@baylibre.com> Content-Language: en-US From: David Lechner In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/18/26 10:14 AM, Sabau, Radu bogdan wrote: >> -----Original Message----- >> From: David Lechner >> Sent: Saturday, May 16, 2026 8:53 PM > > ... > >>> static ssize_t sampling_frequency_show(struct device *dev, >>> struct device_attribute *attr, >>> char *buf) >>> @@ -880,6 +1229,9 @@ static ssize_t sampling_frequency_show(struct >> device *dev, >>> struct iio_dev *indio_dev = dev_to_iio_dev(dev); >>> struct ad4691_state *st = iio_priv(indio_dev); >>> >>> + if (st->manual_mode && st->offload) >>> + return sysfs_emit(buf, "%llu\n", READ_ONCE(st->offload- >>> trigger_hz)); >> >> Why do we need READ_ONCE? >> > > trigger_hz is u64 and if the target is 32-bit, a 64-bit access compiles to two 32-bit > instructions, so show() reading it without a lock and store() writing it concurrently > can produce a torn value at the compiler level. READ_ONCE/WRITE_ONCE suppress > the compiler transformations that would allow that splitting or caching. We could > have st->lock in show() instead, but that felt heavier than necessary for a single > scalar where a transiently stale-but-whole read is fine. > I would go with the mutex. It will be easier for people to understand.