linux-kernel - Re: [RFCv2 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

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Date:	Wed, 21 Jan 2015 17:31:28 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Sumit Semwal <sumit.semwal@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	t.stanislaws@...sung.com, linaro-kernel@...ts.linaro.org,
	robdclark@...il.com, daniel@...ll.ch, m.szyprowski@...sung.com
Subject: Re: [RFCv2 2/2] dma-buf: add helpers for sharing attacher
 constraints with dma-parms

On Wed, Jan 21, 2015 at 09:46:47AM +0530, Sumit Semwal wrote:
> +static int calc_constraints(struct device *dev,
> +			    struct dma_buf_constraints *calc_cons)
> +{
> +	struct dma_buf_constraints cons = *calc_cons;
> +
> +	cons.dma_mask &= dma_get_mask(dev);

I don't think this makes much sense when you consider that the DMA
infrastructure supports buses with offsets.  The DMA mask is th
upper limit of the _bus_ specific address, it is not a mask per-se.

What this means is that &= is not the right operation.  Moreover,
simply comparing masks which could be from devices on unrelated
buses doesn't make sense either.

However, that said, I don't have an answer for what you want to
achieve here.

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