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Mon, 03 Aug 2026 12:42:50 -0700 (PDT) Received: from systembl0wer ([2a02:8308:4092:11f0::f9f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49807b5b4a2sm305796885e9.1.2026.08.03.12.42.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Aug 2026 12:42:50 -0700 (PDT) Date: Mon, 3 Aug 2026 21:42:48 +0200 From: Joshua Crofts To: sashiko-bot@kernel.org Cc: sashiko-reviews@lists.linux.dev, robh@kernel.org, conor+dt@kernel.org, devicetree@vger.kernel.org, jic23@kernel.org, dlechner@baylibre.com, andy@kernel.org, nuno.sa@analog.com, linux-iio@vger.kernel.org Subject: Re: [PATCH v3 2/2] iio: dac: mcp47a1: add support for new device Message-ID: <20260803214248.69c3c96b@systembl0wer> In-Reply-To: <20260803174441.294171F000E9@smtp.kernel.org> References: <20260803-mcp47a1-add-support-v3-0-540e71b4fd2e@gmail.com> <20260803-mcp47a1-add-support-v3-2-540e71b4fd2e@gmail.com> <20260803174441.294171F000E9@smtp.kernel.org> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 03 Aug 2026 17:44:40 +0000 sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [Medium] Incorrect SMBus commands send extra bytes and corrupt the DAC hardware state. > -- > > --- Patch [2]: [PATCH v3 2/2] iio: dac: mcp47a1: add support for new device --- > commit f73263d5ea24798a693c0c4cfa738627794988ba > Author: Joshua Crofts > > iio: dac: mcp47a1: add support for new device > > This commit introduces a new driver for the Microchip MCP47A1 6-bit volatile > DAC. It supports writing and reading the raw values and exposing the scale > using I2C. > > > diff --git a/drivers/iio/dac/mcp47a1.c b/drivers/iio/dac/mcp47a1.c > > new file mode 100644 > > index 0000000000000..0bf994aa0e4f5 > > --- /dev/null > > +++ b/drivers/iio/dac/mcp47a1.c > > [ ... ] > > > +static int mcp47a1_write(struct iio_dev *indio_dev, > > + struct iio_chan_spec const *chan, > > + int val, int val2, long mask) > > +{ > > + struct mcp47a1_data *data = iio_priv(indio_dev); > > + > > + switch (mask) { > > + case IIO_CHAN_INFO_RAW: > > + if (!in_range(val, 0, MCP47A1_MAX_STEPS)) > > + return -EINVAL; > > + > > + return i2c_smbus_write_byte_data(data->client, MCP47A1_CMD_CODE, > > + val); > > [Severity: Medium] > Could this corrupt the DAC hardware state by sending an extra byte? > > If the MCP47A1 expects a single byte without a command code, using > i2c_smbus_write_byte_data() will send a 2-byte payload, writing 0x00 to the > DAC before the actual value. This could potentially cause an output glitch. > > > + default: > > + return -EINVAL; > > + } > > +} > > + > > +static int mcp47a1_read(struct iio_dev *indio_dev, > > + struct iio_chan_spec const *chan, > > + int *val, int *val2, long mask) > > +{ > > + struct mcp47a1_data *data = iio_priv(indio_dev); > > + int ret; > > + > > + switch (mask) { > > + case IIO_CHAN_INFO_RAW: > > + ret = i2c_smbus_read_byte_data(data->client, MCP47A1_CMD_CODE); > > [Severity: Medium] > Does this destructively reset the DAC on every read? > > If the device does not expect a command code and interprets it as a data byte, > calling i2c_smbus_read_byte_data() will perform a write of 0x00 before reading, > destructively resetting the DAC output to 0. No, this is a false positive. The MCP47A1 is SMBus compatible, it will interpret the command as an instruction, not a data byte. -- Kind regards, Joshua Crofts