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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id r22-20020a056870581600b001324315bb6asm11365614oap.29.2022.10.21.21.04.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Oct 2022 21:04:15 -0700 (PDT) Sender: Guenter Roeck Message-ID: <7de80d4f-7c25-6b6b-ebb0-e9e1254dac53@roeck-us.net> Date: Fri, 21 Oct 2022 21:04:14 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.2.2 Subject: Re: [PATCH v3 1/2] hwmon: (jc42) Convert register access and caching to regmap/regcache Content-Language: en-US To: Martin Blumenstingl Cc: linux-hwmon@vger.kernel.org, jdelvare@suse.com, linux-kernel@vger.kernel.org References: <20221021165000.1865615-1-martin.blumenstingl@googlemail.com> <20221021165000.1865615-2-martin.blumenstingl@googlemail.com> <20221021171127.GB1888515@roeck-us.net> From: Guenter Roeck In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/21/22 10:51, Martin Blumenstingl wrote: > Hi Guenter, > > On Fri, Oct 21, 2022 at 7:11 PM Guenter Roeck wrote: > [...] >>> @@ -368,17 +361,14 @@ static int jc42_write(struct device *dev, enum hwmon_sensor_types type, >>> } >>> data->config = (data->config & ~JC42_CFG_HYST_MASK) | >>> (hyst << JC42_CFG_HYST_SHIFT); >>> - ret = i2c_smbus_write_word_swapped(data->client, >>> - JC42_REG_CONFIG, >>> - data->config); >>> + ret = regmap_write(data->regmap, JC42_REG_CONFIG, >>> + data->config); >>> break; >> >> This code sequence still requires a mutex since another thread could modify >> the upper limit (and/or the hysteresis) while the hysteresis is in the process >> of being written. Worst case there could be a mismatch between the value in >> data->config and the value actually written into the chip. Granted, that is >> unlikely to happen, but the race still exists. > Thanks for spotting this - this is indeed a potential issue. > Do you also want me to add locking for the data->config access (read) > in jc42_read()? Without a lock there in theory jc42_write() may have > already updated data->config with a new value while hardware still has > the old value. So in the end the read output may show a hysteresis > which was not programmed to the registers at that time. > Thanks for noticing. I had missed that one. Yes, please. Thanks, Guenter