Hi Harsh,
On 26/03/18 10:55, Harsh Jain wrote:
Hi,
Can we add offset to dma address received from IOMMU in scatter/Gather list
before sending it to H/W.
Address to HW = sg_dma_address(sg) + offset, where 0 < offset < sg_dma_len(sg).
sg_dma_address() should already account for sg->offset (i.e. the start
of the buffer within the page. If there's a DMA API implementation
failing to respect that then that's a bug.
I need this operation to make sure our H/W does not receives entry of size
greater than 2K.
If however it's just that you want to fragment a single SG entry into
multiple commaneds/descriptors/etc. internally to your driver, then I
can't see that being an issue as long as you don't visibly modify the
scatterlist itself. If there's a genuine length and/or alignment
limitation in the hardware, though, it would be better to set up
dev->dma_parms appropriately to describe them, such that the subsystem
responsible for generating the scatterlist respects the appropriate
constraints in the first place (and if it doesn't, then that's another
bug to fix).
Robin.
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