linux-kernel - Re: [PATCH v5 0/7] iio: introduce IIO_DECLARE_BUFFER_WITH

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Message-ID: <20250507205454.56cbf6e2@jic23-huawei>
Date: Wed, 7 May 2025 20:54:54 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: David Lechner <dlechner@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Lars-Peter Clausen
 <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, Eugen
 Hristev <eugen.hristev@...aro.org>, Nicolas Ferre
 <nicolas.ferre@...rochip.com>, Alexandre Belloni
 <alexandre.belloni@...tlin.com>, Claudiu Beznea <claudiu.beznea@...on.dev>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, Trevor Gamblin
 <tgamblin@...libre.com>
Subject: Re: [PATCH v5 0/7] iio: introduce IIO_DECLARE_BUFFER_WITH_TS

On Wed, 07 May 2025 07:39:07 +0100
Nuno Sá <noname.nuno@...il.com> wrote:

> On Mon, 2025-05-05 at 11:31 -0500, David Lechner wrote:
> > Creating a buffer of the proper size and correct alignment for use with
> > iio_push_to_buffers_with_ts() is commonly used and not easy to get
> > right (as seen by a number of recent fixes on the mailing list).
> > 
> > In general, we prefer to use this pattern for creating such buffers:
> > 
> > struct {
> >     u16 data[2];
> >     aligned_s64 timestamp;
> > } buffer;
> > 
> > However, there are many cases where a driver may have a large number of
> > channels that can be optionally enabled or disabled in a scan or the
> > driver might support a range of chips that have different numbers of
> > channels or different storage sizes for the data. In these cases, the
> > timestamp may not always be at the same place relative to the data. To
> > handle these, we allocate a buffer large enough for the largest possible
> > case and don't care exactly where the timestamp ends up in the buffer.
> > 
> > For these cases, we propose to introduce new macros to make it easier
> > it easier for both the authors to get it right and for readers of the
> > code to not have to do all of the math to verify that it is correct.
> > 
> > I have just included a few examples of drivers that can make use of this
> > new macro, but there are dozens more.
> > 
> > ---  
> 
> LGTM
> 
> Reviewed-by: Nuno Sá <nuno.sa@...log.com>

Thanks,

Still time for additional comments, but given where we are in the
cycle I'm keen to get this at least undergoing build tests.

Applied to the togreg branch of iio.git and pushed out as testing for
those build tests.

Thanks,

Jonathan

> 
> > Changes in v5:
> > - Add new patch to set minimum alignment to 8 for IIO_DMA_MINALIGN.
> > - Adjust IIO_DECLARE_DMA_BUFFER_WITH_TS() macro for above change.
> > - Drop one ad4695 patch that was already applied.
> > - Link to v4:
> > https://lore.kernel.org/r/20250428-iio-introduce-iio_declare_buffer_with_ts-v4-0-6f7f6126f1cb@baylibre.com
> > 
> > Changes in v4:
> > - Dropped static_assert()s from the first patch.
> > - Handle case when IIO_DMA_MINALIGN < sizeof(timestamp).
> > - Added one more patch for ad4695 to rename a confusing macro.
> > - Link to v3:
> > https://lore.kernel.org/r/20250425-iio-introduce-iio_declare_buffer_with_ts-v3-0-f12df1bff248@baylibre.com
> > 
> > Changes in v3:
> > - Fixed a few mistakes, style issues and incorporate other feedback (see
> >   individual commit message changelogs for details).
> > - Link to v2:
> > https://lore.kernel.org/r/20250422-iio-introduce-iio_declare_buffer_with_ts-v2-0-3fd36475c706@baylibre.com
> > 
> > Changes in v2:
> > - Add 2nd macro for case where we need DMA alignment.
> > - Add new patch for ad4695 to convert buffer from u8 to u16 before
> >   making use of the new macro.
> > - Drop the bmp280 patch since it was determined to have a better
> >   alternative not using these macros.
> > - Add a few more examples to show the non-DMA case, both in a struct and
> >   stack allocated.
> > - Link to v1:
> > https://lore.kernel.org/r/20250418-iio-introduce-iio_declare_buffer_with_ts-v1-0-ee0c62a33a0f@baylibre.com
> > 
> > ---
> > David Lechner (7):
> >       iio: make IIO_DMA_MINALIGN minimum of 8 bytes
> >       iio: introduce IIO_DECLARE_BUFFER_WITH_TS macros
> >       iio: adc: ad4695: use IIO_DECLARE_DMA_BUFFER_WITH_TS
> >       iio: adc: ad4695: rename AD4695_MAX_VIN_CHANNELS
> >       iio: adc: ad7380: use IIO_DECLARE_DMA_BUFFER_WITH_TS
> >       iio: accel: sca3300: use IIO_DECLARE_BUFFER_WITH_TS
> >       iio: adc: at91-sama5d2: use IIO_DECLARE_BUFFER_WITH_TS
> > 
> >  drivers/iio/accel/sca3300.c        | 18 ++--------------
> >  drivers/iio/adc/ad4695.c           | 11 +++++-----
> >  drivers/iio/adc/ad7380.c           |  3 +--
> >  drivers/iio/adc/at91-sama5d2_adc.c | 13 ++----------
> >  include/linux/iio/iio.h            | 42 ++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 52 insertions(+), 35 deletions(-)
> > ---
> > base-commit: 7e9a82ab5b861d3c33c99a22c1245a5b262ee502
> > change-id: 20250418-iio-introduce-iio_declare_buffer_with_ts-2f8773f7dad6
> > 
> > Best regards,  
>