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[98.183.112.25]) by smtp.gmail.com with ESMTPSA id 5614622812f47-3febf6dce65sm62432b6e.14.2025.03.20.13.43.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Mar 2025 13:43:02 -0700 (PDT) Message-ID: <4fb5329f-be34-4d98-b34e-2da4e035f44c@baylibre.com> Date: Thu, 20 Mar 2025 15:43:00 -0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/5] iio: adc: ad400: Set transfer bits_per_word to have data in CPU endianness To: Marcelo Schmitt , linux-iio@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: jic23@kernel.org, lars@metafoo.de, Michael.Hennerich@analog.com, corbet@lwn.net, marcelo.schmitt1@gmail.com References: <930560a0d0ca7af597d4ad901422bc9ba3fc6a79.1742394806.git.marcelo.schmitt@analog.com> From: David Lechner Content-Language: en-US In-Reply-To: <930560a0d0ca7af597d4ad901422bc9ba3fc6a79.1742394806.git.marcelo.schmitt@analog.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/19/25 9:57 AM, Marcelo Schmitt wrote: > When SPI `bits_per_word` is not set, SPI transfers default 8-bit word size > and ADC data gets stored in big-endian format in memory. Because of that, > the IIO driver requests ADC data to be rearranged from BE to CPU > endianness. However, with `bits_per_word` set to the number of ADC > precision bits, transfers use larger word sizes that get stored in > 'in-memory wordsizes' and can be read in CPU endianness. > > Use proper `bits_per_word` size for SPI transfers thus saving the driver > from requesting endianness conversions. With that, shifting the buffer > data is also no longer needed. This change has no impact on IIO device > functionality. > > Signed-off-by: Marcelo Schmitt > --- This is a breaking change. Some SPI controllers, like RPi can only do 8-bit transfers, so this driver would stop working on those platforms. Also, if anyone made software already that depended on the big-endian ordering without checking the scan_type attribute, it would break that software. I would leave this as-is (drop this patch) and just make it: .endianness = _offl ? IIO_CPU : IIO_BE, in the next patch.