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

[Mayuresh Chitale]

Hi Zane,
On Sun, Sep 20, 2026 at 4:28 PM Zane Leung <liangzhen@xxxxxxxxxxxxxxxxxx> wrote:
>
>
> 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.
I think we can set stop_on_wrap later but mode must be set during prob.e
>
> > +     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");