Re: [PATCH v5 09/14] gtrace: Add RISC-V Trace ramsink driver

[Zane Leung]

On 8/10/2026 11:22 PM, Mayuresh Chitale wrote:
> Add initial implementation of RISC-V E-Trace ramsink driver. The ramsink
> is defined in the RISC-V Trace Control Interface specification.
>
> Co-developed-by: Anup Patel <anup.patel@xxxxxxxxxxxxxxxx>
> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxxxxxxxx>
> Signed-off-by: Mayuresh Chitale <mayuresh.chitale@xxxxxxxxxxxxxxxx>
> ---
>  drivers/hwtracing/gtrace/Kconfig           |  15 +
>  drivers/hwtracing/gtrace/Makefile          |   1 +
>  drivers/hwtracing/gtrace/rvtrace-ramsink.c | 320 +++++++++++++++++++++
>  3 files changed, 336 insertions(+)
>  create mode 100644 drivers/hwtracing/gtrace/rvtrace-ramsink.c
>
> diff --git a/drivers/hwtracing/gtrace/Kconfig b/drivers/hwtracing/gtrace/Kconfig
> index e3a621b59913..de4a3b533591 100644
> --- a/drivers/hwtracing/gtrace/Kconfig
> +++ b/drivers/hwtracing/gtrace/Kconfig
> @@ -41,3 +41,18 @@ config RVTRACE_ENCODER
>  
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called rvtrace-encoder.
> +
> +config RVTRACE_RAMSINK
> +	tristate "RISC-V Trace Ramsink driver"
> +	depends on RVTRACE
> +	select DMA_SHARED_BUFFER
> +	default y
> +	help
> +	  This driver provides support for the RISC-V trace ramsink component
> +	  which is defined by the RISC-V Trace Control Interface specification.
> +	  The ramsink is a trace sink which stores the trace data generated by
> +	  the upstream components into a system memory buffer. The buffer is
> +	  then copied to the perf AUX buffer when tracing using the perf tool.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rvtrace-ramsink.
> diff --git a/drivers/hwtracing/gtrace/Makefile b/drivers/hwtracing/gtrace/Makefile
> index 10a74f852115..3e0c68d1b632 100644
> --- a/drivers/hwtracing/gtrace/Makefile
> +++ b/drivers/hwtracing/gtrace/Makefile
> @@ -5,3 +5,4 @@ gtrace-y := gtrace-core.o
>  
>  obj-$(CONFIG_RVTRACE) += rvtrace-platform.o
>  obj-$(CONFIG_RVTRACE_ENCODER) += rvtrace-encoder.o
> +obj-$(CONFIG_RVTRACE_RAMSINK) += rvtrace-ramsink.o
> diff --git a/drivers/hwtracing/gtrace/rvtrace-ramsink.c b/drivers/hwtracing/gtrace/rvtrace-ramsink.c
> new file mode 100644
> index 000000000000..7ed25cf364a7
> --- /dev/null
> +++ b/drivers/hwtracing/gtrace/rvtrace-ramsink.c
> @@ -0,0 +1,320 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2026 Qualcomm Technologies, Inc.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/gtrace.h>
> +#include <linux/types.h>
> +#include <linux/sizes.h>
> +#include <uapi/linux/perf_event.h>
> +#include "rvtrace.h"
> +
> +#define RVTRACE_RAMSINK_STARTLOW_OFF		0x010
> +#define RVTRACE_RAMSINK_STARTHIGH_OFF		0x014
> +#define RVTRACE_RAMSINK_LIMITLOW_OFF		0x018
> +#define RVTRACE_RAMSINK_LIMITHIGH_OFF		0x01c
> +#define RVTRACE_RAMSINK_WPLOW_OFF		0x020
> +#define RVTRACE_RAMSINK_WPHIGH_OFF		0x024
> +#define RVTRACE_RAMSINK_WPLOW_WRAP		0x1
> +#define RVTRACE_RAMSINK_CTRL_MODE_SHIFT		0x4
> +#define RVTRACE_RAMSINK_CTRL_STP_WRAP_SHIFT	0x8
> +
> +enum rvtrace_ramsink_mode {
> +	MODE_SRAM,
> +	MODE_SMEM
> +};
> +
> +struct rvtrace_ramsink_priv {
> +	size_t size;
> +	void *va;
> +	dma_addr_t start;
> +	dma_addr_t end;
> +	enum rvtrace_ramsink_mode mode;
> +	bool stop_on_wrap;
> +	int mem_acc_width;
> +	u64 prev_wp;
> +};
> +
> +struct trace_buf {
> +	void *base;
> +	size_t cur;
> +	size_t len;
> +};
> +
> +static int rvtrace_ramsink_start(struct gtrace_component *comp)
> +{
> +	int ret;
> +
> +	ret = gtrace_enable_component(comp);
> +	if (ret)
> +		dev_err(&comp->dev, "failed to start ramsink.\n");
> +
> +	return ret;
> +}
> +
> +static int rvtrace_ramsink_stop(struct gtrace_component *comp)
> +{
> +	int ret;
> +
> +	ret = gtrace_disable_component(comp);
> +	if (ret) {
> +		dev_err(&comp->dev, "failed to stop ramsink.\n");
> +		return ret;
> +	}
> +
> +	return rvtrace_comp_poll_empty(comp);
> +}
> +
> +static void tbuf_to_pbuf_copy(struct trace_buf *src, struct trace_buf *dst, size_t size)
> +{
> +	int bytes_dst, bytes_src, bytes;
> +	void *dst_addr, *src_addr;
> +
> +	/* If destination cannot hold entire source buffer then write only the latest data. */
> +	if (dst->len < size) {
> +		src->cur = (src->cur + size - dst->len) % src->len;
> +		size = dst->len;
> +	}
> +
> +	while (size) {
> +		src_addr = src->base + src->cur;
> +		dst_addr = dst->base + dst->cur;
> +
> +		/* Ensure that there are no OOB memory accesses */
> +		if (dst->len - dst->cur < size)
> +			bytes_dst = dst->len - dst->cur;
> +		else
> +			bytes_dst = size;
> +
> +		if (src->len - src->cur < size)
> +			bytes_src = src->len - src->cur;
> +		else
> +			bytes_src = size;
> +		bytes = bytes_dst < bytes_src ? bytes_dst : bytes_src;
> +		memcpy(dst_addr, src_addr, bytes);
> +		dst->cur = (dst->cur + bytes) % dst->len;
> +		src->cur = (src->cur + bytes) % src->len;
> +		size -= bytes;
> +	}
> +}
> +
> +static size_t rvtrace_ramsink_copyto_auxbuf(struct gtrace_component *comp,
> +					    struct gtrace_perf_auxbuf *buf,
> +					    u64 *format)
> +{
> +	struct rvtrace_ramsink_priv *priv = dev_get_drvdata(&comp->dev);
> +	struct trace_buf src, dst;
> +	u32 wp_low, wp_high;
> +	size_t bytes = 0;
> +	bool wrap;
> +	u64 wp;
> +
> +	dst.base = buf->base;
> +	dst.len = buf->length;
> +	dst.cur = buf->pos;
> +	src.base = priv->va;
> +	src.len = priv->size;
> +	wp_low = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_WPLOW_OFF);
> +	wp_high = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_WPHIGH_OFF);
> +	wp = (u64)(wp_high) << 32 | wp_low;
> +	wrap = wp & RVTRACE_RAMSINK_WPLOW_WRAP;
> +	wp &= ~RVTRACE_RAMSINK_WPLOW_WRAP;
> +	if (wrap) {
> +		gtrace_write32(comp->pdata, lower_32_bits(priv->start),
> +				RVTRACE_RAMSINK_WPLOW_OFF);
> +		gtrace_write32(comp->pdata, upper_32_bits(priv->start),
> +				RVTRACE_RAMSINK_WPHIGH_OFF);
> +		src.cur = wp - priv->start;
> +		priv->prev_wp = priv->start;
> +		/*
> +		 * There is no way to tell if trRamWp wrapped around more than once. As a
> +		 * result priv->prev_wp can't be used and the entire buffer must be copied
> +		 * even though some data might be duplicated.
> +		 */
> +		bytes = priv->size;
> +	} else {
> +		src.cur =  priv->prev_wp - priv->start;
> +		bytes = wp - priv->prev_wp;
> +		priv->prev_wp = wp;
> +	}
> +
> +	tbuf_to_pbuf_copy(&src, &dst, bytes);
> +	dev_dbg(&comp->dev, "Copied %zu bytes\n", bytes);
> +	*format = PERF_AUX_FLAG_GTRACE_FORMAT_ETRACE;
> +	return bytes;
> +}
> +
> +static int rvtrace_ramsink_setup_buf(struct gtrace_component *comp,
> +				     struct rvtrace_ramsink_priv *priv)
> +{
> +	struct device *pdev = comp->pdata->dev;
> +	u64 start_min, limit_max, end;
> +	u32 low, high;
> +	int ret;
> +
> +	/* Probe min and max values for start and limit registers */
> +	gtrace_write32(comp->pdata, 0, RVTRACE_RAMSINK_STARTLOW_OFF);
> +	gtrace_write32(comp->pdata, 0, RVTRACE_RAMSINK_STARTHIGH_OFF);
> +	low = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_STARTLOW_OFF);
> +	high = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_STARTHIGH_OFF);
> +	start_min = (u64)(high) << 32 | low;
> +
> +	gtrace_write32(comp->pdata, 0xffffffff, RVTRACE_RAMSINK_LIMITLOW_OFF);
> +	gtrace_write32(comp->pdata, 0xffffffff, RVTRACE_RAMSINK_LIMITHIGH_OFF);
> +	low = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_LIMITLOW_OFF);
> +	high = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_LIMITHIGH_OFF);
> +	limit_max = (u64)(high) << 32 | low;
> +
> +	/* Set DMA mask based on the maximum allowed limit address */
> +	ret = dma_set_mask_and_coherent(pdev, DMA_BIT_MASK(fls64(limit_max)));
> +	if (ret)
> +		return ret;
> +
> +	priv->va = dma_alloc_coherent(pdev, priv->size, &priv->start, GFP_KERNEL);
> +	if (!priv->va)
> +		return -ENOMEM;
> +
> +	priv->end = priv->start + priv->size;
> +	priv->prev_wp = priv->start;
> +	if (priv->end <= start_min || priv->start >= limit_max) {
> +		dma_free_coherent(pdev, priv->size, priv->va, priv->start);
> +		dev_err(&comp->dev, "DMA memory not addressable by device\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Setup ram sink start addresses */
> +	if (priv->start < start_min) {
> +		dev_warn(&comp->dev, "Ramsink start address updated from %pad to %pad\n",
> +			 &priv->start, &start_min);
> +		priv->va += start_min - priv->start;
> +		priv->start = start_min;
> +	}
> +
> +	gtrace_write32(comp->pdata, lower_32_bits(priv->start), RVTRACE_RAMSINK_STARTLOW_OFF);
> +	gtrace_write32(comp->pdata, upper_32_bits(priv->start), RVTRACE_RAMSINK_STARTHIGH_OFF);
> +	gtrace_write32(comp->pdata, lower_32_bits(priv->start), RVTRACE_RAMSINK_WPLOW_OFF);
> +	gtrace_write32(comp->pdata, upper_32_bits(priv->start), RVTRACE_RAMSINK_WPHIGH_OFF);
> +	/* Setup ram sink limit addresses */
> +	if (priv->end > limit_max) {
> +		dev_warn(&comp->dev, "Ramsink limit address updated from %pad to %pad\n",
> +			 &priv->end, &limit_max);
> +		priv->end = limit_max;
> +		priv->size = priv->end - priv->start;
> +	}
> +
> +	/* Limit address needs to be set to end - mem_access_width to avoid overflow */
> +	end = priv->end - priv->mem_acc_width;
> +	gtrace_write32(comp->pdata, lower_32_bits(end), RVTRACE_RAMSINK_LIMITLOW_OFF);
> +	gtrace_write32(comp->pdata, upper_32_bits(end), RVTRACE_RAMSINK_LIMITHIGH_OFF);
> +	low = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_LIMITLOW_OFF);
> +	high = gtrace_read32(comp->pdata, RVTRACE_RAMSINK_LIMITHIGH_OFF);
> +	end = (u64)(high) << 32 | low;
> +	if (end != (priv->end - 4)) {
> +		dev_warn(&comp->dev, "Ramsink limit address updated from %pad to %pad\n",
> +			 &priv->end, &end);
> +		priv->end = end;
> +		priv->size = priv->end - priv->start;
> +	}
> +
> +	return 0;
> +}
> +
> +static int rvtrace_ramsink_setup(struct gtrace_component *comp)
> +{
> +	struct rvtrace_ramsink_priv *priv;
> +	u32 trram_ctrl;
> +	int ret;
> +
> +	priv = devm_kzalloc(&comp->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	/* Derive RAM sink memory size based on component implementation ID */
> +	switch (comp->pdata->impid) {
> +	default:
> +		priv->size = SZ_1M;
> +		priv->mode = MODE_SMEM;
> +		priv->stop_on_wrap = false;
> +		priv->mem_acc_width = 4;
> +		break;
> +	}
> +

I think `trram_ctrl` should not be written during the `probe`. We may modify `rvtrace_ramsink_priv`

through sysfs or perf events.

> +	trram_ctrl = gtrace_read32(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	trram_ctrl |= priv->mode << RVTRACE_RAMSINK_CTRL_MODE_SHIFT;
> +	gtrace_write32(comp->pdata, trram_ctrl, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	trram_ctrl = gtrace_read32(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	dev_dbg(&comp->dev, "mode: %s\n", (trram_ctrl >> RVTRACE_RAMSINK_CTRL_MODE_SHIFT) & 0x1 ?
> +		 "SMEM" : "SRAM");
> +
> +	trram_ctrl |= priv->stop_on_wrap << RVTRACE_RAMSINK_CTRL_STP_WRAP_SHIFT;
> +	gtrace_write32(comp->pdata, trram_ctrl, RVTRACE_COMPONENT_CTRL_OFFSET);
> +
> +	ret = rvtrace_ramsink_setup_buf(comp, priv);
> +	if (!ret)
> +		dev_set_drvdata(&comp->dev, priv);
> +
> +	return ret;
> +}
> +
> +static void rvtrace_ramsink_cleanup(struct gtrace_component *comp)
> +{
> +	struct rvtrace_ramsink_priv *priv = dev_get_drvdata(&comp->dev);
> +
> +	dma_free_coherent(comp->pdata->dev, priv->size, priv->va, priv->start);
> +}
> +
> +static int rvtrace_ramsink_probe(struct gtrace_component *comp)
> +{
> +	int ret;
> +
> +	ret = rvtrace_ramsink_setup(comp);
> +	if (ret)
> +		return dev_err_probe(&comp->dev, ret, "failed to setup ramsink.\n");
> +
> +	return ret;
> +}
> +
> +static void rvtrace_ramsink_remove(struct gtrace_component *comp)
> +{
> +	rvtrace_ramsink_cleanup(comp);
> +}
> +
> +static const struct gtrace_component_id rvtrace_ramsink_ids[] = {
> +	{ .type = GTRACE_RVTRACE_RAMSINK,
> +	  .version = rvtrace_component_mkversion(1, 0), },
> +	{},
> +};
> +
> +static struct gtrace_driver rvtrace_ramsink_driver = {
> +	.id_table = rvtrace_ramsink_ids,
> +	.copyto_auxbuf = rvtrace_ramsink_copyto_auxbuf,
> +	.stop = rvtrace_ramsink_stop,
> +	.start = rvtrace_ramsink_start,
> +	.probe = rvtrace_ramsink_probe,
> +	.remove = rvtrace_ramsink_remove,
> +	.driver = {
> +		.name = "rvtrace-ramsink",
> +	},
> +};
> +
> +static int __init rvtrace_ramsink_init(void)
> +{
> +	return gtrace_register_driver(&rvtrace_ramsink_driver);
> +}
> +
> +static void __exit rvtrace_ramsink_exit(void)
> +{
> +	gtrace_unregister_driver(&rvtrace_ramsink_driver);
> +}
> +
> +module_init(rvtrace_ramsink_init);
> +module_exit(rvtrace_ramsink_exit);
> +
> +/* Module information */
> +MODULE_AUTHOR("Mayuresh Chitale");
> +MODULE_DESCRIPTION("RISC-V E-Trace Ramsink Driver");
> +MODULE_LICENSE("GPL");