From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C54AB2561B9; Mon, 7 Apr 2025 18:49:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744051785; cv=none; b=OIFhV4kQSrVxZr3Mz5CTs7toWcF9TDLdqN2OtXs5Yi5bA5C7Ic7+nMndMRUB4xkDMv1J8YNVftIlfjbBI1Pv0i546chCmOlt6KprrUvDHd7Lw0QPxw3St+E3kZtJs5G8+ioT12EQoR01WLWff0mtbf3t+uCrn0uKJx0MvVzyvz8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744051785; c=relaxed/simple; bh=DBR6tIZcX9SUviEcWkcmXfotauokDmL7FEuYM/rfV74=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=qa2zoyvptegJCOKKA06lw+3mJ93bAXi1YeLw5RNKfBxdcS7qRW73GoB8HSN1Qf8XDMKZlXr4yfB4AbW1ODMJz8YzQINyYifQX6XVi6DiMCjEV2E/BqCt87dN2hod13HqqhW8Zj1azl1ltMLmtMamWB3AsrE97hFAOMW+ZPalEEs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TMgoJ5ut; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TMgoJ5ut" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E6291C4CEDD; Mon, 7 Apr 2025 18:49:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744051785; bh=DBR6tIZcX9SUviEcWkcmXfotauokDmL7FEuYM/rfV74=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TMgoJ5utj/EVTXZU/G6ORYKhsQn7vjf8a9p+cAMJQRzSAoautoqPv9lMChKUpjZiM nJf0pygyhAMNxjkdk46joUqQFhBco2V3KvHN/38kwRyKmkvbEN/5usNbi9Z3jLPUAL fpCpfv6NZ1Xz7yYAaAZPUPGDQq9Or0FC9tpuuvZT8kUzJ803cQ4hgLqIYS3QIFESER Aw4uRz3I0VO7TTwM5TqTvJQweyVFGmMGMMulfdQullwOJhs6vPa1ZHYRKRIiHOVezk NjXsdV/qlDronbZnSC81sGGNpj0nFhq3GXpoks1qlbZRb/+ljOS1JdTDEV6dFck5Cd Qm24Q+X1vmpow== Date: Mon, 7 Apr 2025 19:49:37 +0100 From: Jonathan Cameron To: Matti Vaittinen Cc: David Lechner , Matti Vaittinen , Lars-Peter Clausen , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Nuno Sa , Javier Carrasco , linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/7] iio: adc: ti-adc128s052: Simplify using be16_to_cpu() Message-ID: <20250407194937.097b7709@jic23-huawei> In-Reply-To: <4f099833-5aa6-47cc-917c-7a466cb644b9@gmail.com> References: <4c3e0d23-2582-4acf-8e90-542c8f8c385f@baylibre.com> <1189b539-adb4-46f9-9783-c6577b57a304@gmail.com> <20250405182947.06d5e67f@jic23-huawei> <4f099833-5aa6-47cc-917c-7a466cb644b9@gmail.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.48; x86_64-pc-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, 7 Apr 2025 08:23:07 +0300 Matti Vaittinen wrote: > On 05/04/2025 20:29, Jonathan Cameron wrote: > > On Thu, 3 Apr 2025 08:16:43 +0300 > > Matti Vaittinen wrote: > > > >> On 03/04/2025 00:04, David Lechner wrote: > >>> On 4/2/25 1:09 AM, Matti Vaittinen wrote: > >>>> The register data is 12-bit big-endian data. Use be16_to_cpu() to do > >>>> the conversion, and simple bitwise AND for masking to make it more > >>>> obvious. > >>>> > >>>> Signed-off-by: Matti Vaittinen > >>>> --- > >>>> Revision history: > >>>> v1 => v2: > >>>> - Fix commit msg to reflect the fact there was no bug > >>>> - Drop Fixes tag > >>>> - Use union for rx / tx buffer to avoid casting > >>>> - Keep the shared message protected by the mutex > >>>> --- > >>>> drivers/iio/adc/ti-adc128s052.c | 18 ++++++++++-------- > >>>> 1 file changed, 10 insertions(+), 8 deletions(-) > >>>> > >>>> diff --git a/drivers/iio/adc/ti-adc128s052.c b/drivers/iio/adc/ti-adc128s052.c > >>>> index a456ea78462f..3e69a5fce010 100644 > >>>> --- a/drivers/iio/adc/ti-adc128s052.c > >>>> +++ b/drivers/iio/adc/ti-adc128s052.c > >>>> @@ -28,32 +28,34 @@ struct adc128 { > >>>> struct regulator *reg; > >>>> struct mutex lock; > >>>> > >>>> - u8 buffer[2] __aligned(IIO_DMA_MINALIGN); > >>>> + union { > >>>> + __be16 rx_buffer; > >>>> + u8 tx_buffer[2]; > > As below. Maybe > > __be16 buffer16; > > u8 buffer[2]; > > Ok. > > >>>> + } __aligned(IIO_DMA_MINALIGN); > >>>> }; > >>>> > >>>> static int adc128_adc_conversion(struct adc128 *adc, u8 channel) > >>>> { > >>>> int ret; > >>>> + char *msg = &adc->tx_buffer[0]; > >>>> > >>>> mutex_lock(&adc->lock); > >>>> > >>>> - adc->buffer[0] = channel << 3; > >>>> - adc->buffer[1] = 0; > >>>> + msg[0] = channel << 3; > >>>> + msg[1] = 0; > >>>> > >>>> - ret = spi_write(adc->spi, &adc->buffer, 2); > >>>> + ret = spi_write(adc->spi, msg, sizeof(adc->tx_buffer)); > > > > I'd get rid of msg as it's now just confusing given we are > > using the sizeof() here. > > Ok. > > >>>> if (ret < 0) { > >>>> mutex_unlock(&adc->lock); > >>>> return ret; > >>>> } > >>>> > >>>> - ret = spi_read(adc->spi, &adc->buffer, 2); > >>>> - > >>>> + ret = spi_read(adc->spi, &adc->rx_buffer, 2); > > > > sizeof(adc->rx_buffer) > > I was thinking of this but went with raw 2 - because we need to read > exactly 2 bytes from the device. Sizeof buffer is matter of software > where as the 2 bytes is dictated by the device. (Sure the size of buffer > needs to be large enough). > > I don't care it that much though, so I can go with the sizeof() if > that's what you prefer. Just explaining that the '2' here was a > conscious choice :) Hmm. If we have a case where we read less than 2 bytes into that buffer then fair enough. Otherwise it's correctly sized so having sizeof(buffer) and having to check that size in only one place is a tiny bit preferable. > > >>>> mutex_unlock(&adc->lock); > >>>> - > >>>> if (ret < 0) > >>>> return ret; > >>>> > >>>> - return ((adc->buffer[0] << 8 | adc->buffer[1]) & 0xFFF); > >>>> + return be16_to_cpu(adc->rx_buffer) & 0xFFF; > >>> > >>> > >>> The cast isn't exactly beautiful, but this would save a lot of > >>> lines of diff and a few lines of code by avoiding the need for > >>> the union and the local msg variable. > >>> > >>> return be16_to_cpup((__be16 *)adc->buffer) & 0xFFF; > > > > The cast only works because we have forced the alignment for DMA safety. > > That to me is a little fragile. > > > > You could do get_unaligned_be16() which doesn't need the cast then carry > > on using the original buffer. > >> > >> Thanks again for the review David :) > >> > >> I am unsure which way to go. I kind of like having the __be16 in the > >> struct, as it immediately yells "data from device is big-endian". OTOH, > >> I've never loved unions (and, it silences the above "yelling" quite a > >> bit). I still think this might be the first time I really see a valid > >> use-case for an union :) And, you're right this adds more lines, > >> besides, the cast doesn't look that ugly to me. Yet, I originally had a > >> cast probably as simple as this (and I also had the __be16 in the > >> struct), and Jonathan suggested using union to avoid it... > >> > >> At the end of the day, I suppose I am Okay with any of these 3 > >> approaches. Original cast, union or this cast you suggest. Jonathan, any > >> preferences on your side? > > > > Majority of the diff is really about renaming buffer to tx_buffer. > > Could just not bother doing that and instead have buffer and buffer16 > > as the two union elements. With msg gone as suggested above, then the diff > > becomes only a few lines and you get to keep the nicety of it being either > > a pair of u8s or a __be16. > > I was tempted to try using the spi_write_then_read() - but I suppose > this may be kind of a hot path. Given it's small, I doubt it would make any noticeable difference in performance. > > I'll go with (not)renaming the buffer and dropping the msg, to squeeze > the diff. Works for me. J > > Yours, > -- Matti