Re: [PATCH v2] spi: qup: Add DMA capabilities

[Mark Brown <broonie@kernel.org>]

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On Tue, Feb 24, 2015 at 03:00:03PM +0200, Stanimir Varbanov wrote:

> +static void spi_qup_dma_done(void *data)
> +{
> +	struct spi_qup *qup = data;
> +
> +	if (atomic_dec_and_test(&qup->dma_outstanding))
> +		complete(&qup->done);
> +}

I'm finding it hard to be thrilled about the use of atomics for
synchronization (they're just generally hard to work with) and...

> +	cookie = dmaengine_submit(desc);
> +	ret = dma_submit_error(cookie);
> +	if (ret)
> +		return ret;

> +	atomic_inc(&qup->dma_outstanding);

..don't we have two potential races here: one if somehow the DMA manages
to complete prior to the atomic_inc() (unlikely but that's what race
conditions are all about really) and one if we are issuing multiple DMAs
and the early ones complete before the later ones are issued?

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