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 3C14D1E231E; Sun, 27 Apr 2025 10:20:45 +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=1745749247; cv=none; b=d/H/3J2fumWUrFydJ34I3un7qiQbDTsZg3U5GkIEbcqbtygM5s2p5L0teQo4EY8oyIapRb0f8dPmn2f3D/522FsenzhsCxoAEiVSDGH1pLog550LjYjfQMDqjnLqZjKlhG4F0Zldvbh5Fx9RwvLAFxLrOfSzd7EKRHeqJnOAdfg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745749247; c=relaxed/simple; bh=UvgX/22nEMLGVHnLX7utgwefDV5CfKGMP+fQPcGv4Q8=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=fhcBrFpZTrnvApp6XtW+TFkYeY+BMagWhoQ73dHT/LzeW34eW9wFvmZjL6/WgJxOEg3VHyeNaOyQrHUmpnqwmvMFbnMtJfizvyc5tyXnUOWlf9+RJiUvz/ON244mmRL8FKGkD13mbZsMIrSyuRe46z+vZ0QVPVjDVSFRGbCZE5s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Mc+LLps/; 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="Mc+LLps/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C48CEC4CEE3; Sun, 27 Apr 2025 10:20:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745749245; bh=UvgX/22nEMLGVHnLX7utgwefDV5CfKGMP+fQPcGv4Q8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Mc+LLps/OnHxQfbiaghh+dEvxoV3Tu6fQOxBLkQ/rdYm27bU20RcLqL3a9YmusXM5 CS+/188Z1gv96pms5EKq1PJ/3ynRurt6g+z1sZVQLY4Sr/E8ke8RMIANy4VNuY8ZtU O/csuIRW74bWlRCxv5qi1miUsupmS1z4uxFcnk5cxEkrjiXFxtQcZTZB/YR1zsqizi VcddKI4RMtewnXSIjbuFWddJ/+x8n8F/uB1mLjc1nPmqEoZ4yi+AiSFtA2oTvaJf+A efRx5rTreJQNcidxZ9jMT8nyWtVu38+aKrM1rtQI3Z9BvOF6Lo6LDdzsT6udCocyyk tsRD8/vZCyVsg== Date: Sun, 27 Apr 2025 11:20:35 +0100 From: Jonathan Cameron To: David Lechner Cc: Nuno =?UTF-8?B?U8Oh?= , Andy Shevchenko , Lars-Peter Clausen , Michael Hennerich , Eugen Hristev , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 1/6] iio: introduce IIO_DECLARE_BUFFER_WITH_TS macros Message-ID: <20250427112035.112d086d@jic23-huawei> In-Reply-To: <8a57a332-c2a6-4825-a5f7-d765ea15bd6f@baylibre.com> References: <20250425-iio-introduce-iio_declare_buffer_with_ts-v3-0-f12df1bff248@baylibre.com> <20250425-iio-introduce-iio_declare_buffer_with_ts-v3-1-f12df1bff248@baylibre.com> <20250426123509.0b04f0f9@jic23-huawei> <8a57a332-c2a6-4825-a5f7-d765ea15bd6f@baylibre.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.48; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-iio@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 Sat, 26 Apr 2025 17:34:10 -0500 David Lechner wrote: > On 4/26/25 6:35 AM, Jonathan Cameron wrote: > > On Fri, 25 Apr 2025 16:08:43 -0500 > > David Lechner wrote: > > > > ... > > >> @@ -777,6 +779,42 @@ static inline void *iio_device_get_drvdata(const struct iio_dev *indio_dev) > >> * them safe for use with non-coherent DMA. > >> */ > >> #define IIO_DMA_MINALIGN ARCH_DMA_MINALIGN > >> + > >> +#define __IIO_DECLARE_BUFFER_WITH_TS(type, name, count) \ > >> + static_assert(count); \ > > > > Why do we care if count is 0? Or is intent to check if is constant? > > If the thought is we don't care either way about 0 (as rather nonsensical) > > and this will fail to compile if not constant, then perhaps a comment would > > avoid future confusion? > > I would be inclined to just leave out the check. But yes, it is just checking > that count is constant and we don't expect 0. > > > > >> + type name[ALIGN((count), sizeof(s64) / sizeof(type)) + sizeof(s64) / sizeof(type)] > >> + > >> +/** > >> + * IIO_DECLARE_BUFFER_WITH_TS() - Declare a buffer with timestamp > >> + * @type: element type of the buffer > >> + * @name: identifier name of the buffer > >> + * @count: number of elements in the buffer > >> + * > >> + * Declares a buffer that is safe to use with iio_push_to_buffer_with_ts(). In > >> + * addition to allocating enough space for @count elements of @type, it also > >> + * allocates space for a s64 timestamp at the end of the buffer and ensures > >> + * proper alignment of the timestamp. > >> + */ > >> +#define IIO_DECLARE_BUFFER_WITH_TS(type, name, count) \ > >> + __IIO_DECLARE_BUFFER_WITH_TS(type, name, count) __aligned(sizeof(s64)) > >> + > >> +/** > >> + * IIO_DECLARE_DMA_BUFFER_WITH_TS() - Declare a DMA-aligned buffer with timestamp > >> + * @type: element type of the buffer > >> + * @name: identifier name of the buffer > >> + * @count: number of elements in the buffer > >> + * > >> + * Same as IIO_DECLARE_BUFFER_WITH_TS(), but is uses __aligned(IIO_DMA_MINALIGN) > >> + * to ensure that the buffer doesn't share cachelines with anything that comes > >> + * before it in a struct. This should not be used for stack-allocated buffers > >> + * as stack memory cannot generally be used for DMA. > >> + */ > >> +#define IIO_DECLARE_DMA_BUFFER_WITH_TS(type, name, count) \ > >> + __IIO_DECLARE_BUFFER_WITH_TS(type, name, count) __aligned(IIO_DMA_MINALIGN) > >> + > >> +static_assert(IIO_DMA_MINALIGN % sizeof(s64) == 0, > > That message isn't super helpful if seen in a compile log as we aren't reading the code here > > "IIO_DECLARE_DMA_BUFFER_WITH_TS() assumes that ... > > > >> + "macros above assume that IIO_DMA_MINALIGN also ensures s64 timestamp alignment"); > >> + > > Seems we actually have an arch (openrisc) that triggers this [1]. This arch > doesn't define ARCH_DMA_MINALIGN so it falls back to: > > #define ARCH_DMA_MINALIGN __alignof__(unsigned long long) > > Apparently this is only of those 32-bit arches that only does 4 byte alignment. > From the official docs [2]: > > Current OR32 implementations (OR1200) do not implement 8 byte alignment, > but do require 4 byte alignment. Therefore the Application Binary > Interface (chapter 16) uses 4 byte alignment for 8 byte types. Future > extensions such as ORVDX64 may require natural alignment. > > [1]: https://lore.kernel.org/linux-iio/20250425-iio-introduce-iio_declare_buffer_with_ts-v3-0-f12df1bff248@baylibre.com/T/#m91e0332673438793ff76949037ff40a34765ca30 > [2]: https://openrisc.io/or1k.html > > > It looks like this could work (it compiles for me): > > __aligned(MAX(IIO_DMA_MINALIGN, sizeof(s64))) > > If that is OK we could leave out the static_assert(), unless we think there > could be an arch with IIO_DMA_MINALIGN not a power of 2?! > That change seems fine. Non power of 2 arch would be fun but implausible any time soon :)