linux-kernel - Re: [PATCH 03/16] iio: adc: at91-sama5d2_adc: exit from write

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Message-ID: <20220611183354.08788921@jic23-huawei>
Date:   Sat, 11 Jun 2022 18:33:54 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>
Cc:     <eugen.hristev@...rochip.com>, <lars@...afoo.de>,
        <nicolas.ferre@...rochip.com>, <alexandre.belloni@...tlin.com>,
        <robh+dt@...nel.org>, <krzk+dt@...nel.org>,
        <ludovic.desroches@...el.com>, <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/16] iio: adc: at91-sama5d2_adc: exit from write_raw()
 when buffers are enabled

On Thu, 9 Jun 2022 11:32:00 +0300
Claudiu Beznea <claudiu.beznea@...rochip.com> wrote:

> When buffers are enabled conversion may start asynchronously thus
> allowing changes on actual hardware could lead to bad behavior. Thus
> do not allow changing oversampling ratio and sample frequency when
> buffers are enabled.

Less than desirable behavior perhaps, but broken?  I don't see this
as a fix from what you have mentioned - though I'm not against it.
(just drop the fixes tag)
It is an ABI change, but unlikely to be one any sane code hits.

> 
> Fixes: 5e1a1da0f8c9 ("iio: adc: at91-sama5d2_adc: add hw trigger and buffer support")
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
> ---
>  drivers/iio/adc/at91-sama5d2_adc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iio/adc/at91-sama5d2_adc.c b/drivers/iio/adc/at91-sama5d2_adc.c
> index a672a520cdc0..b76328da0cb2 100644
> --- a/drivers/iio/adc/at91-sama5d2_adc.c
> +++ b/drivers/iio/adc/at91-sama5d2_adc.c
> @@ -1644,6 +1644,9 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
>  {
>  	struct at91_adc_state *st = iio_priv(indio_dev);
>  
> +	if (iio_buffer_enabled(indio_dev))
> +		return -EBUSY;

This is racy as nothing stops buffers being enabled after this point.
Use the iio_device_claim_direct_mode() and release for this as they
protect against the race.


> +
>  	switch (mask) {
>  	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
>  		if ((val != AT91_OSR_1SAMPLES) && (val != AT91_OSR_4SAMPLES) &&