[PATCH] DMA: AT91: Get residual bytes in dma buffer

[Song, Elen]

Ping....

>-----Original Message-----
>From: Song, Elen
>Sent: 2012年10月15日 17:19
>To: Ferre, Nicolas
>Cc: 'Russell King - ARM Linux'; 'Jean-Christophe PLAGNIOL-VILLARD';
>linux-arm-kernel at lists.infradead.org
>Subject: [PATCH] DMA: AT91: Get residual bytes in dma buffer
>
>The main purpose of atc_tx_status is to get residual bytes when dma transfer in
>progress or complete.
>
>Residual bytes is the number of bytes left to read from DMA source.
>During transfer, residual bytes is changing as DMA read from its source.
>When transfer complete, the residual bytes is zero.
>
>atc_get_bytes_left will dynamically get bytes left in dma buffer.
>It reads count register bit btsize to get residue, the btsize only indicate current
>descriptor receive data.
>So we should let atc_get_bytes_left know when descriptor switch or dma
>transfer done.
>DMA_CTRL_ACK is a useful ack, it means current descriptor can not be reused
>when clear.
>The atc_get_bytes_left will find out whether move to next descriptor or transfer
>done.
>
>So in dma handler, we get residue like below:
>dma_handler() {
>        async_tx_clear_ack; //clear ack, tell driver it is time to switch
>descriptor
>        read residue;
>        async_tx_ack; //move to next descriptor
>                        // no need to set ack when dma transfer done }
>
>DMA should be pause so that we can trust data count.
>
>Signed-off-by: Elen Song <elen.song at atmel.com>
>---
> drivers/dma/at_hdmac.c      |  127
>+++++++++++++++++++++++++++++++++++++++----
> drivers/dma/at_hdmac_regs.h |    4 ++
> 2 files changed, 120 insertions(+), 11 deletions(-)
>
>diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c index
>13a02f4..b0aa783 100644
>--- a/drivers/dma/at_hdmac.c
>+++ b/drivers/dma/at_hdmac.c
>@@ -229,6 +229,101 @@ static void atc_dostart(struct at_dma_chan *atchan,
>struct at_desc *first)
> 	vdbg_dump_regs(atchan);
> }
>
>+/*
>+ * atc_get_current_descriptors - get descriptor which equal to
>+ * physical address in DSCR.
>+ * @atchan: the channel we want to start
>+ * @dscr_addr: physical descriptor address in DSCR  */ static struct
>+at_desc *atc_get_current_descriptors(struct at_dma_chan *atchan,
>+							u32 dscr_addr)
>+{
>+	struct at_desc  *desc, *_desc, *child, *desc_cur = NULL;
>+
>+	list_for_each_entry_safe(desc, _desc, &atchan->active_list, desc_node)
>+{
>+
>+		if (desc->lli.dscr == dscr_addr) {
>+			desc_cur = desc;
>+			break;
>+		}
>+
>+		list_for_each_entry(child, &desc->tx_list, desc_node) {
>+
>+			if (child->lli.dscr == dscr_addr) {
>+				desc_cur = child;
>+				break;
>+			}
>+		}
>+	}
>+
>+	return desc_cur;
>+}
>+
>+/*
>+ * atc_get_bytes_left - Get the number of bytes
>+ * residue in dma buffer,
>+ * it is unwise to call this before stopping the channel for
>+ * absolute measures.
>+ * @atchan: the channel we want to start  */ static int
>+atc_get_bytes_left(struct at_dma_chan *atchan) {
>+	struct at_desc *desc_first;
>+	int left = 0, count = 0;
>+	u32 dscr_addr;
>+
>+	/* First descriptor embedds additional information */
>+	desc_first = atc_first_active(atchan);
>+	if (!desc_first)
>+		return -EINVAL;
>+
>+	/* Initialize necessary value in the first time.
>+	 * We use desc_cur to save current descriptor,
>+	 * save_len record residual dma buffer length.
>+	 */
>+	if (!atchan->desc_cur &&
>+	    !atchan->save_len) {
>+		atchan->desc_cur = desc_first;
>+		atchan->save_len = desc_first->len;
>+	}
>+
>+	/* This happend in the end of dma transfer or descriptor switch,
>+	 * during the dma interrupt handler, DMA_CTRL_ACK should be cleared.
>+	 * We trigger this flag to get residual values.
>+	 * To be aware of, two conditions should be taken into consideration:
>+	 * at the end of a dma transfer, or descriptors switch.
>+	 */
>+	if (!(desc_first->txd.flags & DMA_CTRL_ACK)) {
>+		dscr_addr = channel_readl(atchan, DSCR);
>+		/* End of a single or cyclic transfer */
>+		if (dscr_addr == 0 || dscr_addr == desc_first->lli.dscr) {
>+			atchan->desc_cur = NULL;
>+			atchan->save_len = 0;
>+		/* Switch between two descriptor.
>+		 * Current descriptor transfer done.
>+		 * The residual buffer length should reduce current descriptor.
>+		 */
>+		} else {
>+			atchan->desc_cur = atc_get_current_descriptors(atchan,
>+								dscr_addr);
>+			if (!atchan->desc_cur)
>+				return -EINVAL;
>+			atchan->save_len -= (atchan->desc_cur->lli.ctrla
>+						& ATC_BTSIZE_MAX);
>+		}
>+
>+		left = atchan->save_len;
>+	}
>+
>+	/* Get residual value during a descriptor transfer */
>+	if (atchan->desc_cur) {
>+		count = channel_readl(atchan, CTRLA) & ATC_BTSIZE_MAX;
>+		left = atchan->save_len - count;
>+	}
>+
>+	return left;
>+}
>+
> /**
>  * atc_chain_complete - finish work for one transaction chain
>  * @atchan: channel we work on
>@@ -1034,23 +1129,33 @@ atc_tx_status(struct dma_chan *chan,
> 	dma_cookie_t		last_complete;
> 	unsigned long		flags;
> 	enum dma_status		ret;
>-
>-	spin_lock_irqsave(&atchan->lock, flags);
>+	int bytes = 0;
>
> 	ret = dma_cookie_status(chan, cookie, txstate);
>-	if (ret != DMA_SUCCESS) {
>-		atc_cleanup_descriptors(atchan);
>-
>-		ret = dma_cookie_status(chan, cookie, txstate);
>+	/* Residue is zero while transactions complete */
>+	if (ret == DMA_SUCCESS) {
>+		dma_set_residue(txstate, 0);
>+		return ret;
>+	}
>+	/*
>+	 * There's no point calculating the residue if there's
>+	 * no txstate to store the value.
>+	 */
>+	if (!txstate) {
>+		if (atc_chan_is_paused(atchan))
>+			ret = DMA_PAUSED;
>+		return ret;
> 	}
>
>-	last_complete = chan->completed_cookie;
>-	last_used = chan->cookie;
>+	spin_lock_irqsave(&atchan->lock, flags);
>
>-	spin_unlock_irqrestore(&atchan->lock, flags);
>+	/*  Get number of bytes left in the active transactions */
>+	bytes = atc_get_bytes_left(atchan);
>+	if (bytes < 0)
>+		dev_err(chan2dev(chan), "get residue value error\n");
>+	dma_set_residue(txstate, bytes);
>
>-	if (ret != DMA_SUCCESS)
>-		dma_set_residue(txstate, atc_first_active(atchan)->len);
>+	spin_unlock_irqrestore(&atchan->lock, flags);
>
> 	if (atc_chan_is_paused(atchan))
> 		ret = DMA_PAUSED;
>diff --git a/drivers/dma/at_hdmac_regs.h b/drivers/dma/at_hdmac_regs.h index
>116e4ad..ea8d747 100644
>--- a/drivers/dma/at_hdmac_regs.h
>+++ b/drivers/dma/at_hdmac_regs.h
>@@ -226,12 +226,14 @@ enum atc_status {
>  * @save_cfg: configuration register that is saved on suspend/resume cycle
>  * @save_dscr: for cyclic operations, preserve next descriptor address in
>  *             the cyclic list on suspend/resume cycle
>+ * @save_len: to record dma buffer length
>  * @dma_sconfig: configuration for slave transfers, passed via
>DMA_SLAVE_CONFIG
>  * @lock: serializes enqueue/dequeue operations to descriptors lists
>  * @active_list: list of descriptors dmaengine is being running on
>  * @queue: list of descriptors ready to be submitted to engine
>  * @free_list: list of descriptors usable by the channel
>  * @descs_allocated: records the actual size of the descriptor pool
>+ * @desc_cur: current descriptor
>  */
> struct at_dma_chan {
> 	struct dma_chan		chan_common;
>@@ -242,6 +244,7 @@ struct at_dma_chan {
> 	struct tasklet_struct	tasklet;
> 	u32			save_cfg;
> 	u32			save_dscr;
>+	u32			save_len;
> 	struct dma_slave_config dma_sconfig;
>
> 	spinlock_t		lock;
>@@ -251,6 +254,7 @@ struct at_dma_chan {
> 	struct list_head	queue;
> 	struct list_head	free_list;
> 	unsigned int		descs_allocated;
>+	struct at_desc		*desc_cur;
> };
>
> #define	channel_readl(atchan, name) \
>--
>1.7.9.5