linux-kernel - Re: [PATCH v5 2/2] iio: adc: ad4130: add AD4130 driver

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Date:   Thu, 23 Jun 2022 17:39:54 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Cosmin Tanislav <demonsingur@...il.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Cosmin Tanislav <cosmin.tanislav@...log.com>
Subject: Re: [PATCH v5 2/2] iio: adc: ad4130: add AD4130 driver

On Thu, Jun 23, 2022 at 5:27 PM Cosmin Tanislav <demonsingur@...il.com> wrote:
> On 6/20/22 21:29, Andy Shevchenko wrote:
> > On Mon, Jun 20, 2022 at 6:27 PM Cosmin Tanislav <demonsingur@...il.com> wrote:

...

> >> +       /*
> >> +        * DMA (thus cache coherency maintenance) requires the
> >> +        * transfer buffers to live in their own cache lines.
> >> +        */
> >
> > This is a good comment, but what fields does it apply to?
>
> Whatever is below it, grouped together. This is not hard to
> understand.

It's hard to understand what exactly is DMA-aware here. I see only one
buffer that is aligned properly for DMA, the rest are not, except the
case if all of them are going in one DMA transaction. Is this the case
here?

> >> +       u8                      reset_buf[AD4130_RESET_BUF_SIZE] __aligned(IIO_DMA_MINALIGN);

This is aligned.

> >> +       u8                      reg_write_tx_buf[4];

This one is aligned + offset (== AD4130_RESET_BUF_SIZE + 0).

> >> +       u8                      reg_read_tx_buf[1];

This one is aligned + offset (== AD4130_RESET_BUF_SIZE + 0 + 4).

> >> +       u8                      reg_read_rx_buf[3];

This one is aligned + offset (== AD4130_RESET_BUF_SIZE + 0 + 4 + 1).
And this is Rx.

> >> +       u8                      fifo_tx_buf[2];

Here is Tx again which is most likely is not aligned...

> >> +       u8                      fifo_rx_buf[AD4130_FIFO_SIZE *
> >> +                                           AD4130_FIFO_MAX_SAMPLE_SIZE];
> >> +};

-- 
With Best Regards,
Andy Shevchenko