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Mon, 12 May 2025 06:31:16 -0700 (PDT) Received: from legfed1 ([2a00:79c0:632:2600:22ea:3d6a:5919:85f8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-442cd34bd84sm167702805e9.22.2025.05.12.06.31.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 May 2025 06:31:16 -0700 (PDT) Date: Mon, 12 May 2025 15:31:14 +0200 From: Dimitri Fedrau To: Guenter Roeck Cc: dimitri.fedrau@liebherr.com, Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Jean Delvare , linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hwmon@vger.kernel.org Subject: Re: [PATCH] pwm: mc33xs2410: add support for temperature sensors Message-ID: <20250512133114.GA6440@legfed1> References: <20250512-mc33xs2410-hwmon-v1-1-addba77c78f9@liebherr.com> <1bd48694-9760-4e6b-9138-4651d42ff032@roeck-us.net> Precedence: bulk X-Mailing-List: linux-pwm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1bd48694-9760-4e6b-9138-4651d42ff032@roeck-us.net> Hi Guenter, Am Mon, May 12, 2025 at 06:04:33AM -0700 schrieb Guenter Roeck: > On 5/12/25 04:26, Dimitri Fedrau via B4 Relay wrote: > > From: Dimitri Fedrau > > > > The MC33XS2410 provides temperature sensors for the central die temperature > > and the four outputs. Additionally a common temperature warning threshold > > can be configured for the outputs. Add hwmon support for the sensors. > > > > Signed-off-by: Dimitri Fedrau > > --- > > > + > > +static int mc33xs2410_hwmon_read_out_status(struct spi_device *spi, > > + int channel, u16 *val) > > +{ > > + int ret; > > + > > + ret = mc33xs2410_read_reg_diag(spi, MC33XS2410_OUT_STA(channel), val); > > + if (ret < 0) > > + return ret; > > + > > + /* Bits latches high */ > > + return mc33xs2410_read_reg_diag(spi, MC33XS2410_OUT_STA(channel), val); > > Is that double read of the same register needed ? If so, you'll probably > need a lock to prevent it from being executed from multiple threads at the > same time. > > The comment "Bit latches high" doesn't really mean anything to me and doesn't > explain why the register needs to be read twice. > > All bits of the output status registers are latched high. In case there was overtemperature detected, the bit stays set until read once and cleared afterwards. So I need a second read to get the "realtime" status. Otherwise I might end up returning an false positive overtemperature warning. I don't think a lock is really necessary, since I'm only interested in the "realtime" status but not if there was a warning in the past. What do you think ? Will improve the comment. Best regards Dimitri Fedrau