[PATCH for-next 1/4] dmaengine: ti: k3-udma: Use ktime/usleep_range based TX completion check

Peter Ujfalusi
2020-01-27T13:20:50Z

From: Vignesh Raghavendra <vigneshr@ti.com>

In some cases (McSPI for example) the jiffie and delayed_work based
workaround can cause big throughput drop.

Switch to use ktime/usleep_range based implementation to be able
to sustain speed for PDMA based peripherals.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
---
drivers/dma/ti/k3-udma.c | 80 ++++++++++++++++++++++++++--------------
1 file changed, 53 insertions(+), 27 deletions(-)

diff --git a/drivers/dma/ti/k3-udma.c b/drivers/dma/ti/k3-udma.c
index ea79c2df28e0..fb59c869a6a7 100644
--- a/drivers/dma/ti/k3-udma.c
+++ b/drivers/dma/ti/k3-udma.c
@@ -5,6 +5,7 @@
*/

#include <linux/kernel.h>
+#include <linux/delay.h>
#include <linux/dmaengine.h>
#include <linux/dma-mapping.h>
#include <linux/dmapool.h>
@@ -169,7 +170,7 @@ enum udma_chan_state {

struct udma_tx_drain {
struct delayed_work work;
- unsigned long jiffie;
+ ktime_t tstamp;
u32 residue;
};

@@ -946,9 +947,10 @@ static bool udma_is_desc_really_done(struct udma_chan *uc, struct udma_desc *d)
peer_bcnt = udma_tchanrt_read(uc->tchan, UDMA_TCHAN_RT_PEER_BCNT_REG);
bcnt = udma_tchanrt_read(uc->tchan, UDMA_TCHAN_RT_BCNT_REG);

+ /* Transfer is incomplete, store current residue and time stamp */
if (peer_bcnt < bcnt) {
uc->tx_drain.residue = bcnt - peer_bcnt;
- uc->tx_drain.jiffie = jiffies;
+ uc->tx_drain.tstamp = ktime_get();
return false;
}

@@ -961,35 +963,59 @@ static void udma_check_tx_completion(struct work_struct *work)
tx_drain.work.work);
bool desc_done = true;
u32 residue_diff;
- unsigned long jiffie_diff, delay;
+ ktime_t time_diff;
+ unsigned long delay;
+
+ while (1) {
+ if (uc->desc) {
+ /* Get previous residue and time stamp */
+ residue_diff = uc->tx_drain.residue;
+ time_diff = uc->tx_drain.tstamp;
+ /*
+ * Get current residue and time stamp or see if
+ * transfer is complete
+ */
+ desc_done = udma_is_desc_really_done(uc, uc->desc);
+ }

- if (uc->desc) {
- residue_diff = uc->tx_drain.residue;
- jiffie_diff = uc->tx_drain.jiffie;
- desc_done = udma_is_desc_really_done(uc, uc->desc);
- }
-
- if (!desc_done) {
- jiffie_diff = uc->tx_drain.jiffie - jiffie_diff;
- residue_diff -= uc->tx_drain.residue;
- if (residue_diff) {
- /* Try to guess when we should check next time */
- residue_diff /= jiffie_diff;
- delay = uc->tx_drain.residue / residue_diff / 3;
- if (jiffies_to_msecs(delay) < 5)
- delay = 0;
- } else {
- /* No progress, check again in 1 second */
- delay = HZ;
+ if (!desc_done) {
+ /*
+ * Find the time delta and residue delta w.r.t
+ * previous poll
+ */
+ time_diff = ktime_sub(uc->tx_drain.tstamp,
+ time_diff) + 1;
+ residue_diff -= uc->tx_drain.residue;
+ if (residue_diff) {
+ /*
+ * Try to guess when we should check
+ * next time by calculating rate at
+ * which data is being drained at the
+ * peer device
+ */
+ delay = (time_diff / residue_diff) *
+ uc->tx_drain.residue;
+ } else {
+ /* No progress, check again in 1 second */
+ schedule_delayed_work(&uc->tx_drain.work, HZ);
+ break;
+ }
+
+ usleep_range(ktime_to_us(delay),
+ ktime_to_us(delay) + 10);
+ continue;
}

- schedule_delayed_work(&uc->tx_drain.work, delay);
- } else if (uc->desc) {
- struct udma_desc *d = uc->desc;
+ if (uc->desc) {
+ struct udma_desc *d = uc->desc;
+
+ uc->bcnt += d->residue;
+ udma_start(uc);
+ vchan_cookie_complete(&d->vd);
+ break;
+ }

- uc->bcnt += d->residue;
- udma_start(uc);
- vchan_cookie_complete(&d->vd);
+ break;
}
}

--
Peter