linux-kernel - Re: [PATCH v6 3/8] iio: accel: adxl313: add buffered FIFO watermark with interrupt handling

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Message-ID: <CAFXKEHYS2rRYtPShU-yyEetQQoo+EbCscjUUGcWdWJQA2UwiYA@mail.gmail.com>
Date: Tue, 1 Jul 2025 09:23:26 +0200
From: Lothar Rubusch <l.rubusch@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: dlechner@...libre.com, nuno.sa@...log.com, andy@...nel.org, corbet@....net, 
	lucas.p.stankus@...il.com, lars@...afoo.de, Michael.Hennerich@...log.com, 
	bagasdotme@...il.com, linux-iio@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 3/8] iio: accel: adxl313: add buffered FIFO watermark
 with interrupt handling

On Sat, Jun 28, 2025 at 7:16 PM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Sun, 22 Jun 2025 12:29:32 +0000
> Lothar Rubusch <l.rubusch@...il.com> wrote:
>
> > Cover the following tasks:
> > - Add scan_mask and scan_index to the IIO channel configuration. The
> > scan_index sets up buffer usage. According to the datasheet, the ADXL313
> > uses a 13-bit wide data field in full-resolution mode. Set the
> > signedness, number of storage bits, and endianness accordingly.
> >
> > - Parse the devicetree for an optional interrupt line and configure the
> > interrupt mapping based on its presence. If no interrupt line is
> > specified, keep the FIFO in bypass mode as currently implemented.
> >
> > - Set up the interrupt handler. Add register access to detect and
> > evaluate interrupts. Implement functions to clear status registers and
> > reset the FIFO.
> >
> > - Implement FIFO watermark configuration and handling. Allow the
> > watermark level to be set, evaluate the corresponding interrupt, read
> > the FIFO contents, and push the data to the IIO channel.
> >
> > Signed-off-by: Lothar Rubusch <l.rubusch@...il.com>
> Hi Lothar,
>

Hi Jonathan, there's still one thing about this patch [PATCH v6 3/8],
I wanted to address:

        struct mutex    lock; /* lock to protect transf_buf */
+       u8 watermark;
        __le16          transf_buf __aligned(IIO_DMA_MINALIGN);
+       __le16          fifo_buf[ADXL313_NUM_AXIS * ADXL313_FIFO_SIZE + 1];
 };

Is this correct usage of the IIO_DMA_MINALIGN? My intention here is to
have transf_buf and fifo_buf[...] aligned with the IIO_DMA_MINALIGN.

Sorry, I should have asked this earlier. I saw the sensor operating,
but I'm unsure if perhaps DMA usage is setup correctly. Perhaps you
could drop me a line of feedback here?

Best,
L