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Thu, 12 Nov 2026 14:10:31 -0800 (PST) Received: from kapoor.iiserb.ac.in ([203.18.51.239]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-379565d07b3sm1079471eec.22.2026.11.12.14.10.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Nov 2026 14:10:30 -0800 (PST) From: Arnav Kapoor To: Jonathan Cameron Cc: David Lechner , =?UTF-8?q?Nuno=20S=C3=A1?= , Andy Shevchenko , Andy Shevchenko , Gwendal Grignou , Stephen Boyd , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] iio: proximity: sx9360: fix hardware gain encoding Date: Fri, 13 Nov 2026 03:40:25 +0530 Message-ID: <20261112221025.509996-1-kapoorarnav43@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107191409.0e4acaad@jic23-hlaptop> References: <20261107112335.444813-1-kapoorarnav43@gmail.com> <20261107191409.0e4acaad@jic23-hlaptop> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Sat, Nov 07, 2026 at 07:14:09PM +0000, Jonathan Cameron wrote: > The default value is odd. Do we have any idea what is in that top bit? > I'm going to guess something harmless and that perhaps the gain value > due to writing a 0 is either rejected, or actually mapped to same as 1. > > You are correct that we really need someone with datasheet access to > sanity check this sone. I still don't have the datasheet, but I found the vendor driver, which is the closest thing I have. Samsung's Android kernels carry an sx9360 driver with a Semtech copyright, for example: https://github.com/TeamWin/android_kernel_samsung_d2q/blob/master/drivers/sensors/sx9360.c It decodes the same field like this: gain = (gain & 0x38) >> 3; if (gain > 0 && gain < 5) /* prints "x%u", 1 << (gain - 1) */ else /* prints "Reserved" */ so codes 1 to 4 are gains 1 to 8 and 0 is reserved, which is what the RFC does. Its init table writes 0x09 to PROXCTRL0_PHR and _PHM, i.e. gain code 1 (x1) with bit 7 clear. That doesn't say what bit 7 does, but the vendor's own default doesn't set it, so I think 0x80 is the same typo as in sx9324 rather than something intentional. It also doesn't say what the hardware does with code 0. Sashiko flagged the same off-by-one on v2 and v3 of the write_gain() series, though that is by the same analogy with the sx9324 fix, so it isn't independent evidence. If this is enough to go on, I'll respin the RFC as a patch on top of v3 of that series, which needs SX9360_REG_PROX_CTRL0_GAIN_8 to become 0x4. Gwendal, Stephen, a confirmation from the datasheet would still be very welcome. Thanks, Arnav