[PATCH v2 1/2] dma: at_hdmac: Fix calculation of the residual bytes

From: Torsten Fleischer
Date: Thu Feb 19 2015 - 12:09:55 EST

From: Torsten Fleischer <torfl6749@xxxxxxxxx>

This patch fixes the following issues regarding to the calculation of the
residue:

1. The residue is always calculated for the current transfer even if the
cookie is associated to a pending transfer.

2. For scatter/gather DMA the calculation of the residue for the current
transfer doesn't include the bytes of the child descriptors that are already
transferred.
It only calculates the difference between the transfer's total length minus
the number of bytes that are already transferred for the current child
descriptor.
For example: There is a scatter/gather DMA transfer with a total length of
1 MByte. Getting the residue several times while the transfer is running shows
something like that:

1: residue = 975584
2: residue = 1002766
3: residue = 992627
4: residue = 983767
5: residue = 985694
6: residue = 1008094
7: residue = 1009741
8: residue = 1011195

3. The driver stores the residue but never resets it when starting a new
transfer.
For example: If there are two subsequent DMA transfers. The first one with
a total length of 1 MByte and the second one with a total length of 1 kByte.
Getting the residue for both transfers shows something like that:

transfer 1: residue = 975584
transfer 2: residue = 1048380

Changes from V1:
* Fixed coding style of the multi-line comments.
* Improved accuracy of the residue calculation when the transfer for the
first descriptor is active.

Signed-off-by: Torsten Fleischer <torfl6749@xxxxxxxxx>
---
drivers/dma/at_hdmac.c | 155 +++++++++++++++++++++++---------------------
drivers/dma/at_hdmac_regs.h | 11 ++--
2 files changed, 87 insertions(+), 79 deletions(-)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index ca9dd26..f46d86d 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -233,93 +233,104 @@ static void atc_dostart(struct at_dma_chan *atchan, struct at_desc *first)
}

/*
- * atc_get_current_descriptors -
- * locate the descriptor which equal to physical address in DSCR
- * @atchan: the channel we want to start
- * @dscr_addr: physical descriptor address in DSCR
+ * atc_get_desc_by_cookie - get the descriptor of a cookie
+ * @atchan: the DMA channel
+ * @cookie: the cookie to get the descriptor for
*/
-static struct at_desc *atc_get_current_descriptors(struct at_dma_chan *atchan,
- u32 dscr_addr)
+static struct at_desc *atc_get_desc_by_cookie(struct at_dma_chan *atchan,
+ dma_cookie_t cookie)
{
- struct at_desc *desc, *_desc, *child, *desc_cur = NULL;
+ struct at_desc *desc, *_desc;

- 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_safe(desc, _desc, &atchan->queue, desc_node) {
+ if (desc->txd.cookie == cookie)
+ return desc;
+ }

- list_for_each_entry(child, &desc->tx_list, desc_node) {
- if (child->lli.dscr == dscr_addr) {
- desc_cur = child;
- break;
- }
- }
+ list_for_each_entry_safe(desc, _desc, &atchan->active_list, desc_node) {
+ if (desc->txd.cookie == cookie)
+ return desc;
}

- return desc_cur;
+ return NULL;
}

-/*
- * atc_get_bytes_left -
- * Get the number of bytes residue in dma buffer,
- * @chan: the channel we want to start
+/**
+ * atc_get_bytes_left - get the number of bytes residue for a cookie
+ * @chan: DMA channel
+ * @cookie: transaction identifier to check status of
*/
-static int atc_get_bytes_left(struct dma_chan *chan)
+static int atc_get_bytes_left(struct dma_chan *chan, dma_cookie_t cookie)
{
struct at_dma_chan *atchan = to_at_dma_chan(chan);
- struct at_dma *atdma = to_at_dma(chan->device);
- int chan_id = atchan->chan_common.chan_id;
struct at_desc *desc_first = atc_first_active(atchan);
- struct at_desc *desc_cur;
+ struct at_desc *desc;
int ret = 0, count = 0;
+ u32 ctrla, dscr;

/*
- * Initialize necessary values in the first time.
- * remain_desc record remain desc length.
+ * If the cookie doesn't match to the currently running transfer then
+ * we can return the total length of the associated DMA transfer,
+ * because it is still queued.
*/
- if (atchan->remain_desc == 0)
- /* First descriptor embedds the transaction length */
- atchan->remain_desc = desc_first->len;
+ desc = atc_get_desc_by_cookie(atchan, cookie);
+ if (desc == NULL)
+ return -EINVAL;
+ else if (desc != desc_first)
+ return desc->total_len;

- /*
- * This happens when current descriptor transfer complete.
- * The residual buffer size should reduce current descriptor length.
- */
- if (unlikely(test_bit(ATC_IS_BTC, &atchan->status))) {
- clear_bit(ATC_IS_BTC, &atchan->status);
- desc_cur = atc_get_current_descriptors(atchan,
- channel_readl(atchan, DSCR));
- if (!desc_cur) {
- ret = -EINVAL;
- goto out;
+ /* cookie matches to the currently running transfer */
+ ret = desc_first->total_len;
+
+ if (desc_first->lli.dscr) {
+ /* hardware linked list transfer */
+
+ /*
+ * Calculate the residue by removing the length of the child
+ * descriptors already transferred from the total length.
+ * To get the current child descriptor we can use the value of
+ * the channel's DSCR register and compare it against the value
+ * of the hardware linked list structure of each child
+ * descriptor.
+ */
+
+ ctrla = channel_readl(atchan, CTRLA);
+ rmb(); /* ensure CTRLA is read before DSCR */
+ dscr = channel_readl(atchan, DSCR);
+
+ /* for the first descriptor we can be more accurate */
+ if (desc_first->lli.dscr == dscr) {
+ count = (ctrla & ATC_BTSIZE_MAX);
+ ret -= count << ATC_REG_TO_SRC_WIDTH(ctrla);
+ return ret;
}

- count = (desc_cur->lli.ctrla & ATC_BTSIZE_MAX)
- << desc_first->tx_width;
- if (atchan->remain_desc < count) {
- ret = -EINVAL;
- goto out;
+ ret -= desc_first->len;
+ list_for_each_entry(desc, &desc_first->tx_list, desc_node) {
+ if (desc->lli.dscr == dscr)
+ break;
+
+ ret -= desc->len;
}

- atchan->remain_desc -= count;
- ret = atchan->remain_desc;
- } else {
/*
- * Get residual bytes when current
- * descriptor transfer in progress.
+ * For the last descriptor in the chain we can calculate
+ * the remaining bytes using the channel's register.
*/
- count = (channel_readl(atchan, CTRLA) & ATC_BTSIZE_MAX)
- << (desc_first->tx_width);
- ret = atchan->remain_desc - count;
+ if (!desc->lli.dscr) {
+ ctrla = channel_readl(atchan, CTRLA);
+ count = (desc->lli.ctrla & ATC_BTSIZE_MAX) -
+ (ctrla & ATC_BTSIZE_MAX);
+
+ ret = count << ATC_REG_TO_SRC_WIDTH(ctrla);
+ }
+ } else {
+ /* single transfer */
+ ctrla = channel_readl(atchan, CTRLA);
+ count = (ctrla & ATC_BTSIZE_MAX) << ATC_REG_TO_SRC_WIDTH(ctrla);
+ ret -= count;
}
- /*
- * Check fifo empty.
- */
- if (!(dma_readl(atdma, CHSR) & AT_DMA_EMPT(chan_id)))
- atc_issue_pending(chan);

-out:
return ret;
}

@@ -534,8 +545,6 @@ static irqreturn_t at_dma_interrupt(int irq, void *dev_id)
/* Give information to tasklet */
set_bit(ATC_IS_ERROR, &atchan->status);
}
- if (pending & AT_DMA_BTC(i))
- set_bit(ATC_IS_BTC, &atchan->status);
tasklet_schedule(&atchan->tasklet);
ret = IRQ_HANDLED;
}
@@ -648,14 +657,14 @@ atc_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
desc->lli.ctrlb = ctrlb;

desc->txd.cookie = 0;
+ desc->len = xfer_count << src_width;

atc_desc_chain(&first, &prev, desc);
}

/* First descriptor of the chain embedds additional information */
first->txd.cookie = -EBUSY;
- first->len = len;
- first->tx_width = src_width;
+ first->total_len = len;

/* set end-of-link to the last link descriptor of list*/
set_desc_eol(desc);
@@ -747,6 +756,7 @@ atc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
| ATC_SRC_WIDTH(mem_width)
| len >> mem_width;
desc->lli.ctrlb = ctrlb;
+ desc->len = len;

atc_desc_chain(&first, &prev, desc);
total_len += len;
@@ -787,6 +797,7 @@ atc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
| ATC_DST_WIDTH(mem_width)
| len >> reg_width;
desc->lli.ctrlb = ctrlb;
+ desc->len = len;

atc_desc_chain(&first, &prev, desc);
total_len += len;
@@ -801,8 +812,7 @@ atc_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,

/* First descriptor of the chain embedds additional information */
first->txd.cookie = -EBUSY;
- first->len = total_len;
- first->tx_width = reg_width;
+ first->total_len = total_len;

/* first link descriptor of list is responsible of flags */
first->txd.flags = flags; /* client is in control of this ack */
@@ -867,6 +877,7 @@ atc_dma_cyclic_fill_desc(struct dma_chan *chan, struct at_desc *desc,
| ATC_FC_MEM2PER
| ATC_SIF(atchan->mem_if)
| ATC_DIF(atchan->per_if);
+ desc->len = period_len;
break;

case DMA_DEV_TO_MEM:
@@ -878,6 +889,7 @@ atc_dma_cyclic_fill_desc(struct dma_chan *chan, struct at_desc *desc,
| ATC_FC_PER2MEM
| ATC_SIF(atchan->per_if)
| ATC_DIF(atchan->mem_if);
+ desc->len = period_len;
break;

default:
@@ -959,8 +971,7 @@ atc_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len,

/* First descriptor of the chain embedds additional information */
first->txd.cookie = -EBUSY;
- first->len = buf_len;
- first->tx_width = reg_width;
+ first->total_len = buf_len;

return &first->txd;

@@ -1091,7 +1102,7 @@ atc_tx_status(struct dma_chan *chan,
spin_lock_irqsave(&atchan->lock, flags);

/* Get number of bytes left in the active transactions */
- bytes = atc_get_bytes_left(chan);
+ bytes = atc_get_bytes_left(chan, cookie);

spin_unlock_irqrestore(&atchan->lock, flags);

@@ -1187,7 +1198,6 @@ static int atc_alloc_chan_resources(struct dma_chan *chan)

spin_lock_irqsave(&atchan->lock, flags);
atchan->descs_allocated = i;
- atchan->remain_desc = 0;
list_splice(&tmp_list, &atchan->free_list);
dma_cookie_init(chan);
spin_unlock_irqrestore(&atchan->lock, flags);
@@ -1230,7 +1240,6 @@ static void atc_free_chan_resources(struct dma_chan *chan)
list_splice_init(&atchan->free_list, &list);
atchan->descs_allocated = 0;
atchan->status = 0;
- atchan->remain_desc = 0;

dev_vdbg(chan2dev(chan), "free_chan_resources: done\n");
}
diff --git a/drivers/dma/at_hdmac_regs.h b/drivers/dma/at_hdmac_regs.h
index 2787aba..f458642 100644
--- a/drivers/dma/at_hdmac_regs.h
+++ b/drivers/dma/at_hdmac_regs.h
@@ -112,11 +112,13 @@
#define ATC_SRC_WIDTH_BYTE (0x0 << 24)
#define ATC_SRC_WIDTH_HALFWORD (0x1 << 24)
#define ATC_SRC_WIDTH_WORD (0x2 << 24)
+#define ATC_REG_TO_SRC_WIDTH(x) (((x) >> 24) & 0x3)
#define ATC_DST_WIDTH_MASK (0x3 << 28) /* Destination Single Transfer Size */
#define ATC_DST_WIDTH(x) ((x) << 28)
#define ATC_DST_WIDTH_BYTE (0x0 << 28)
#define ATC_DST_WIDTH_HALFWORD (0x1 << 28)
#define ATC_DST_WIDTH_WORD (0x2 << 28)
+#define ATC_REG_TO_DST_WIDTH(x) (((x) >> 28) & 0x3)
#define ATC_DONE (0x1 << 31) /* Tx Done (only written back in descriptor) */

/* Bitfields in CTRLB */
@@ -181,8 +183,8 @@ struct at_lli {
* @at_lli: hardware lli structure
* @txd: support for the async_tx api
* @desc_node: node on the channed descriptors list
- * @len: total transaction bytecount
- * @tx_width: transfer width
+ * @len: descriptor byte count
+ * @total_len: total transaction byte count
*/
struct at_desc {
/* FIRST values the hardware uses */
@@ -193,7 +195,7 @@ struct at_desc {
struct dma_async_tx_descriptor txd;
struct list_head desc_node;
size_t len;
- u32 tx_width;
+ size_t total_len;
};

static inline struct at_desc *
@@ -213,7 +215,6 @@ txd_to_at_desc(struct dma_async_tx_descriptor *txd)
enum atc_status {
ATC_IS_ERROR = 0,
ATC_IS_PAUSED = 1,
- ATC_IS_BTC = 2,
ATC_IS_CYCLIC = 24,
};

@@ -231,7 +232,6 @@ 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
- * @remain_desc: to save remain desc 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
@@ -250,7 +250,6 @@ struct at_dma_chan {
struct tasklet_struct tasklet;
u32 save_cfg;
u32 save_dscr;
- u32 remain_desc;
struct dma_slave_config dma_sconfig;

spinlock_t lock;
--
2.1.4

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