dmaengine: omap: add support for returning residue in tx_state method

Add support for returning the residue for a particular descriptor by
reading the current DMA address for the source or destination side of
the transfer as appropriate, and walking the scatterlist until we find
an entry containing the current DMA address.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

drivers/dma/omap-dma.c

@@ -194,14 +194,73 @@ static void omap_dma_free_chan_resources(struct dma_chan *chan)
 	dev_info(c->vc.chan.device->dev, "freeing channel for %u\n", c->dma_sig);
 }
 
+static size_t omap_dma_sg_size(struct omap_sg *sg)
+{
+	return sg->en * sg->fn;
+}
+
+static size_t omap_dma_desc_size(struct omap_desc *d)
+{
+	unsigned i;
+	size_t size;
+
+	for (size = i = 0; i < d->sglen; i++)
+		size += omap_dma_sg_size(&d->sg[i]);
+
+	return size * es_bytes[d->es];
+}
+
+static size_t omap_dma_desc_size_pos(struct omap_desc *d, dma_addr_t addr)
+{
+	unsigned i;
+	size_t size, es_size = es_bytes[d->es];
+
+	for (size = i = 0; i < d->sglen; i++) {
+		size_t this_size = omap_dma_sg_size(&d->sg[i]) * es_size;
+
+		if (size)
+			size += this_size;
+		else if (addr >= d->sg[i].addr &&
+			 addr < d->sg[i].addr + this_size)
+			size += d->sg[i].addr + this_size - addr;
+	}
+	return size;
+}
+
 static enum dma_status omap_dma_tx_status(struct dma_chan *chan,
 	dma_cookie_t cookie, struct dma_tx_state *txstate)
 {
-	/*
-	 * FIXME: do we need to return pending bytes?
-	 * We have no users of that info at the moment...
-	 */
-	return dma_cookie_status(chan, cookie, txstate);
+	struct omap_chan *c = to_omap_dma_chan(chan);
+	struct virt_dma_desc *vd;
+	enum dma_status ret;
+	unsigned long flags;
+
+	ret = dma_cookie_status(chan, cookie, txstate);
+	if (ret == DMA_SUCCESS || !txstate)
+		return ret;
+
+	spin_lock_irqsave(&c->vc.lock, flags);
+	vd = vchan_find_desc(&c->vc, cookie);
+	if (vd) {
+		txstate->residue = omap_dma_desc_size(to_omap_dma_desc(&vd->tx));
+	} else if (c->desc && c->desc->vd.tx.cookie == cookie) {
+		struct omap_desc *d = c->desc;
+		dma_addr_t pos;
+
+		if (d->dir == DMA_MEM_TO_DEV)
+			pos = omap_get_dma_src_pos(c->dma_ch);
+		else if (d->dir == DMA_DEV_TO_MEM)
+			pos = omap_get_dma_dst_pos(c->dma_ch);
+		else
+			pos = 0;
+
+		txstate->residue = omap_dma_desc_size_pos(d, pos);
+	} else {
+		txstate->residue = 0;
+	}
+	spin_unlock_irqrestore(&c->vc.lock, flags);
+
+	return ret;
 }
 
 static void omap_dma_issue_pending(struct dma_chan *chan)