On Sat, 2019-06-08 at 15:21 +0100, Jonathan Cameron wrote:
> [External]
>
>
> On Thu, 30 May 2019 10:59:11 +0300
> Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> wrote:
>
> > This change has a few parts:
> > 1. Remove the buffer from the trigger handler's stack
> > 2. Having it dynamically allocated means it should be cache-aligned
> > 3. The buffer would now adapt to the actual number of bytes needed,
> > whether it's more than 16 bytes, or less
> > 4. Having it in the heap somewhere, allows it to work with DMA
> >
> > This is a fix + enhancement in one.
> >
> > Fixes: af3008485ea03 ("iio: ad_sigma_delta: allocate data dynamically for samples")
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
>
> Comment inline. This is using an element of iio_dev that is marked
> INTERN in the header...
>
> > ---
> > drivers/iio/adc/ad_sigma_delta.c | 12 ++++++++++--
> > include/linux/iio/adc/ad_sigma_delta.h | 2 ++
> > 2 files changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
> > index ec0e38566ece..91d5dda53d29 100644
> > --- a/drivers/iio/adc/ad_sigma_delta.c
> > +++ b/drivers/iio/adc/ad_sigma_delta.c
> > @@ -360,6 +360,11 @@ static int ad_sd_buffer_postenable(struct iio_dev *indio_dev)
> > if (ret)
> > return ret;
> >
> > + kfree(sigma_delta->buf_data);
> > + sigma_delta->buf_data = kzalloc(indio_dev->scan_bytes, GFP_KERNEL);
> Hmm. Another thing that I'm trying to stop drivers doing is accessing elements
> of the struct iio_dev that have been marked in the header as INTERN.
>
> That really restricts the ability to refactor that code.
>
> The argument has always been that a driver ought to be able to 'tell' how
> large a buffer it can conceivably need and often it will actually use
> a 'superset' of that to avoid the need to do additional allocations.
>
> It's a it trickier when there is a generic layer inbetween the driver and
> the core like we have here.
>
> If the below 16 is correct, you are almost certain to not actually see any
> advantage in a separate allocation. So two options come to mind.
>
> 1) Ensure ad_sigma_delta is appropriately aligned in the priv data
> of each driver, then use ___cacheline_aligned on a fixed 16 byte buffer
> in ad_sigma_delta.
> 2) Do the separate allocation, but stick to 16 bytes (you will always
> get more than that anyway as always at least a cacheline - otherwise
> same DMA issue might occur).
Hmmm.
I think I got the gist of it.
I'll take a look and come back.
Thanks
Alex
>
> > + if (!sigma_delta->buf_data)
> > + return -ENOMEM;
> > +
> > spi_bus_lock(sigma_delta->spi->master);
> > sigma_delta->bus_locked = true;
> > sigma_delta->keep_cs_asserted = true;
> > @@ -403,12 +408,12 @@ static irqreturn_t ad_sd_trigger_handler(int irq, void *p)
> > struct iio_poll_func *pf = p;
> > struct iio_dev *indio_dev = pf->indio_dev;
> > struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
> > + uint8_t *data = sigma_delta->buf_data;
> > unsigned int reg_size;
> > unsigned int data_reg;
> > - uint8_t data[16];
> > int ret;
> >
> > - memset(data, 0x00, 16);
> > + memset(data, 0x00, indio_dev->scan_bytes);
> >
> > reg_size = indio_dev->channels[0].scan_type.realbits +
> > indio_dev->channels[0].scan_type.shift;
> > @@ -568,6 +573,9 @@ EXPORT_SYMBOL_GPL(ad_sd_setup_buffer_and_trigger);
> > */
> > void ad_sd_cleanup_buffer_and_trigger(struct iio_dev *indio_dev)
> > {
> > + struct ad_sigma_delta *sigma_delta = iio_device_get_drvdata(indio_dev);
> > +
> > + kfree(sigma_delta->buf_data);
> > ad_sd_remove_trigger(indio_dev);
> > iio_triggered_buffer_cleanup(indio_dev);
> > }
> > diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
> > index 6e9fb1932dde..36dc49b8dfd5 100644
> > --- a/include/linux/iio/adc/ad_sigma_delta.h
> > +++ b/include/linux/iio/adc/ad_sigma_delta.h
> > @@ -75,6 +75,8 @@ struct ad_sigma_delta {
> >
> > const struct ad_sigma_delta_info *info;
> >
> > + uint8_t *buf_data;
> > +
> > /*
> > * DMA (thus cache coherency maintenance) requires the
> > * transfer buffers to live in their own cache lines.
