On Mon, 22 May 2023 00:59:00 +0200
Artur Rojek <contact@xxxxxxxxxxxxxx> wrote:
> Consumers expect the buffer to only contain enabled channels. While
> preparing the buffer, the driver makes two mistakes:
> 1) It inserts empty data for disabled channels.
> 2) Each ADC readout contains samples for two 16-bit channels. If either
> of them is active, the whole 32-bit sample is pushed into the buffer
> as-is.
>
> Both of those issues cause the active channels to appear at the wrong
> offsets in the buffer. Fix the above by demuxing samples for active
> channels only.
>
> This has remained unnoticed, as all the consumers so far were only using
> channels 0 and 1, leaving them unaffected by changes introduced in this
> commit.
>
> Signed-off-by: Artur Rojek <contact@xxxxxxxxxxxxxx>
> Tested-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Lazy me suggestions that, as we didn't notice this before, clearly the
vast majority of times the channels are both enabled.
As such you 'could' just set available_scan_masks and burn the overhead
of reading channels you don't want, instead letting the IIO core demux
deal with the data movement if needed.
> ---
>
> v2: - demux active channels from ADC readouts
> - clarify in the commit description that this patch doesn't impact
> existing consumers of this driver
>
> drivers/iio/adc/ingenic-adc.c | 20 +++++++++++++-------
> 1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/iio/adc/ingenic-adc.c b/drivers/iio/adc/ingenic-adc.c
> index a7325dbbb99a..093710a7ad4c 100644
> --- a/drivers/iio/adc/ingenic-adc.c
> +++ b/drivers/iio/adc/ingenic-adc.c
> @@ -802,13 +802,19 @@ static irqreturn_t ingenic_adc_irq(int irq, void *data)
> struct ingenic_adc *adc = iio_priv(iio_dev);
> unsigned long mask = iio_dev->active_scan_mask[0];
> unsigned int i;
> - u32 tdat[3];
> -
> - for (i = 0; i < ARRAY_SIZE(tdat); mask >>= 2, i++) {
> - if (mask & 0x3)
> - tdat[i] = readl(adc->base + JZ_ADC_REG_ADTCH);
> - else
> - tdat[i] = 0;
> + u16 tdat[6];
> + u32 val;
> +
> + memset(tdat, 0, ARRAY_SIZE(tdat));
> + for (i = 0; mask && i < ARRAY_SIZE(tdat); mask >>= 2) {
> + if (mask & 0x3) {
> + val = readl(adc->base + JZ_ADC_REG_ADTCH);
> + /* Two channels per sample. Demux active. */
> + if (mask & BIT(0))
> + tdat[i++] = val & 0xffff;
> + if (mask & BIT(1))
> + tdat[i++] = val >> 16;
> + }
> }
>
> iio_push_to_buffers(iio_dev, tdat);
