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[90.182.112.124]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f273195d9sm2408390f8f.3.2026.07.10.01.51.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Jul 2026 01:51:11 -0700 (PDT) Date: Fri, 10 Jul 2026 10:51:09 +0200 From: Joshua Crofts To: Mert Seftali Cc: Jonathan Cameron , David Lechner , Nuno =?ISO-8859-1?Q?S=E1?= , Andy Shevchenko , Jelle van der Waa , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] iio: accel: dmard09: Implement IIO_CHAN_INFO_SCALE Message-ID: <20260710105109.000047c5@gmail.com> In-Reply-To: <20260710083623.84243-1-mertsftl@gmail.com> References: <20260710083623.84243-1-mertsftl@gmail.com> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.51; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-kernel@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 Fri, 10 Jul 2026 10:36:23 +0200 Mert Seftali wrote: > Reading the in_accel_scale attribute on the DMARD09 has always returned > -EINVAL: the channels advertise scale via info_mask_shared_by_type so the > IIO core exposes the attribute, but dmard09_read_raw() only handles > IIO_CHAN_INFO_RAW, so a SCALE read falls through to 'default: return > -EINVAL': > > $ cat .../iio:deviceX/in_accel_scale > cat: in_accel_scale: Invalid argument > > leaving userspace with raw counts it cannot convert to m/s^2. > > The driver was written from a vendor source [1] without a datasheet, and > the scale was declared but never implemented. The vendor source carries > the sensitivity: its conversion is > > acc = raw * GRAVITY_EARTH_1000 / sensitivity (then / 1000 -> m/s^2) > > with sensitivity = 32 and GRAVITY_EARTH_1000 = 9807 ("about > (9.80665)*1000"), i.e. 32 counts correspond to 1 g. > > That sensitivity applies to the value this driver already reports as raw: > the vendor reduces each 16-bit sample to a signed 9-bit value, and the > preparation in dmard09_read_raw() yields the same value. It is > self-consistent: 256 counts / 32 = 8 g full scale, matching the +/-8g > range. > > Implement the scale derived from that sensitivity using standard gravity: > > scale = 9.80665 / 32 = 0.3064578125 m/s^2 per LSB > > Link: https://github.com/minstrelsy/mediatek/blob/1f49d8c87b839651bc89afc870277e8e0f2e2d55/custom/common/kernel/accelerometer/dmard09/dmard09.c [1] > Fixes: a4fa6509dda4 ("iio: accel: add support for the Domintech DMARD09 3-axis accelerometer") > Signed-off-by: Mert Seftali > --- Good thing that Jelle sent the vendor driver, LGTM. Reviewed-by: Joshua Crofts -- Kind regards CJD