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Message-ID: <20250528-mchp-tcb-dma-v1-2-083a41fb7b51@microchip.com>
Date: Wed, 28 May 2025 11:43:05 +0530
From: Dharma Balasubiramani <dharma.b@...rochip.com>
To: Kamel Bouhara <kamel.bouhara@...tlin.com>, William Breathitt Gray
<wbg@...nel.org>, Nicolas Ferre <nicolas.ferre@...rochip.com>, "Alexandre
Belloni" <alexandre.belloni@...tlin.com>, Claudiu Beznea
<claudiu.beznea@...on.dev>
CC: <linux-arm-kernel@...ts.infradead.org>, <linux-iio@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, Dharma Balasubiramani
<dharma.b@...rochip.com>
Subject: [PATCH 2/2] counter: microchip-tcb-capture: Add DMA support for
TC_RAB register reads
Add optional DMA-based data transfer support to read the TC_RAB register,
which provides the next unread captured value from either RA or RB. This
improves performance and offloads CPU when mchp,use-dma-cap is enabled in
the device tree.
Signed-off-by: Dharma Balasubiramani <dharma.b@...rochip.com>
---
drivers/counter/microchip-tcb-capture.c | 110 +++++++++++++++++++++++++++++++-
include/soc/at91/atmel_tcb.h | 1 +
2 files changed, 108 insertions(+), 3 deletions(-)
diff --git a/drivers/counter/microchip-tcb-capture.c b/drivers/counter/microchip-tcb-capture.c
index 9634da75bd1a..fa177edc6803 100644
--- a/drivers/counter/microchip-tcb-capture.c
+++ b/drivers/counter/microchip-tcb-capture.c
@@ -6,6 +6,9 @@
*/
#include <linux/clk.h>
#include <linux/counter.h>
+#include <linux/dmaengine.h>
+#include <linux/dma-direction.h>
+#include <linux/dma-mapping.h>
#include <linux/interrupt.h>
#include <linux/mfd/syscon.h>
#include <linux/module.h>
@@ -28,9 +31,19 @@
#define ATMEL_TC_QDEN BIT(8)
#define ATMEL_TC_POSEN BIT(9)
+struct mchp_tc_dma {
+ struct dma_chan *chan;
+ struct dma_slave_config slave_cfg;
+ u32 *buf;
+ dma_addr_t addr;
+ phys_addr_t phy_addr;
+ bool enabled;
+};
+
struct mchp_tc_data {
const struct atmel_tcb_config *tc_cfg;
struct platform_device *pdev;
+ struct mchp_tc_dma dma;
struct regmap *regmap;
void __iomem *base;
int qdec_mode;
@@ -74,6 +87,61 @@ static struct counter_synapse mchp_tc_count_synapses[] = {
}
};
+static void mchp_tc_dma_remove(void *data)
+{
+ struct mchp_tc_data *priv = data;
+
+ if (priv->dma.buf)
+ dma_free_coherent(&priv->pdev->dev, sizeof(u32),
+ priv->dma.buf, priv->dma.addr);
+
+ if (priv->dma.chan)
+ dma_release_channel(priv->dma.chan);
+}
+
+static int mchp_tc_dma_transfer(struct mchp_tc_data *priv, u32 *val)
+{
+ struct dma_async_tx_descriptor *desc;
+ struct device *dev = &priv->pdev->dev;
+ dma_cookie_t cookie;
+ int ret;
+
+ ret = dmaengine_slave_config(priv->dma.chan, &priv->dma.slave_cfg);
+ if (ret) {
+ dev_err(dev, "DMA slave_config failed (%d)\n", ret);
+ return ret;
+ }
+
+ desc = dmaengine_prep_dma_memcpy(priv->dma.chan,
+ priv->dma.addr,
+ priv->dma.slave_cfg.src_addr,
+ sizeof(u32),
+ DMA_CTRL_ACK | DMA_PREP_INTERRUPT);
+ if (!desc) {
+ dev_err(dev, "DMA prep descriptor failed\n");
+ return -ENOMEM;
+ }
+
+ cookie = dmaengine_submit(desc);
+ if (dma_submit_error(cookie)) {
+ dev_err(dev, "DMA submit error (%d)\n", cookie);
+ return cookie ?: -EIO;
+ }
+
+ dma_async_issue_pending(priv->dma.chan);
+
+ ret = dma_sync_wait(priv->dma.chan, cookie);
+ if (ret) {
+ dev_err(dev, "DMA transfer timed out (%d)\n", ret);
+ return ret;
+ }
+
+ /* Retrieve the 32-bit value the engine just copied */
+ *val = le32_to_cpu(*(u32 *)priv->dma.buf);
+
+ return 0;
+}
+
static int mchp_tc_count_function_read(struct counter_device *counter,
struct counter_count *count,
enum counter_function *function)
@@ -260,20 +328,25 @@ static int mchp_tc_count_cap_read(struct counter_device *counter,
struct counter_count *count, size_t idx, u64 *val)
{
struct mchp_tc_data *const priv = counter_priv(counter);
- u32 cnt;
+ u32 cnt, reg_offset;
int ret;
switch (idx) {
case COUNTER_MCHP_EXCAP_RA:
- ret = regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], RA), &cnt);
+ reg_offset = ATMEL_TC_REG((priv->channel[0]), RA);
break;
case COUNTER_MCHP_EXCAP_RB:
- ret = regmap_read(priv->regmap, ATMEL_TC_REG(priv->channel[0], RB), &cnt);
+ reg_offset = ATMEL_TC_REG((priv->channel[0]), RB);
break;
default:
return -EINVAL;
}
+ if (!priv->dma.enabled)
+ ret = regmap_read(priv->regmap, reg_offset, &cnt);
+ else
+ ret = mchp_tc_dma_transfer(priv, &cnt);
+
if (ret < 0)
return ret;
@@ -578,6 +651,7 @@ static int mchp_tc_probe(struct platform_device *pdev)
if (ret)
return ret;
+ priv->dma.phy_addr = parent_res->start;
priv->tc_cfg = tcb_config;
priv->regmap = regmap;
priv->pdev = pdev;
@@ -589,6 +663,36 @@ static int mchp_tc_probe(struct platform_device *pdev)
counter->num_signals = ARRAY_SIZE(mchp_tc_count_signals);
counter->signals = mchp_tc_count_signals;
+ /* Check the dma flag */
+ priv->dma.enabled = of_property_read_bool(np, "mchp,use-dma-cap") ? true : false;
+
+ if (priv->dma.enabled) {
+ /* Initialise DMA */
+ priv->dma.buf = dma_alloc_coherent(&pdev->dev, sizeof(u32),
+ &priv->dma.addr, GFP_KERNEL);
+ if (!priv->dma.buf)
+ return -ENOMEM;
+
+ priv->dma.chan = dma_request_chan(&parent_pdev->dev, "rx");
+ if (IS_ERR(priv->dma.chan))
+ return -EINVAL;
+
+ dev_info(&pdev->dev, "Using %s (rx) for DMA transfers\n",
+ dma_chan_name(priv->dma.chan));
+
+ /* Configure DMA channel to read TC AB register */
+ priv->dma.slave_cfg.direction = DMA_DEV_TO_MEM;
+ priv->dma.slave_cfg.src_addr = priv->dma.phy_addr + ATMEL_TC_REG(priv->channel[0],
+ RAB);
+ priv->dma.slave_cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
+ priv->dma.slave_cfg.src_maxburst = 1;
+ priv->dma.slave_cfg.dst_maxburst = 1;
+
+ ret = devm_add_action_or_reset(&pdev->dev, mchp_tc_dma_remove, priv);
+ if (ret)
+ return ret;
+ }
+
i = of_irq_get(np->parent, 0);
if (i == -EPROBE_DEFER)
return -EPROBE_DEFER;
diff --git a/include/soc/at91/atmel_tcb.h b/include/soc/at91/atmel_tcb.h
index 26b56a07bd1f..9fad7f58a56a 100644
--- a/include/soc/at91/atmel_tcb.h
+++ b/include/soc/at91/atmel_tcb.h
@@ -243,6 +243,7 @@ extern const u8 atmel_tc_divisors[5];
#define ATMEL_TC_RA 0x14 /* register A */
#define ATMEL_TC_RB 0x18 /* register B */
#define ATMEL_TC_RC 0x1c /* register C */
+#define ATMEL_TC_RAB 0x0c /* register AB */
#define ATMEL_TC_SR 0x20 /* status (read-only) */
/* Status-only flags */
--
2.43.0
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