linux-kernel - Re: [PATCH 05/11] rvtrace: Add trace encoder driver

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Message-ID: <793a00d6-a1ae-4928-a326-3d276a30bdbd@gmail.com>
Date: Tue, 7 Oct 2025 00:09:50 -0700
From: Bo Gan <ganboing@...il.com>
To: Anup Patel <apatel@...tanamicro.com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Greg KH <gregkh@...uxfoundation.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Ian Rogers <irogers@...gle.com>
Cc: Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
 Alexandre Ghiti <alex@...ti.fr>, Atish Patra <atish.patra@...ux.dev>,
 Peter Zijlstra <peterz@...radead.org>, Anup Patel <anup@...infault.org>,
 Adrian Hunter <adrian.hunter@...el.com>, linux-kernel@...r.kernel.org,
 Mayuresh Chitale <mchitale@...tanamicro.com>, Ingo Molnar
 <mingo@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
 Mayuresh Chitale <mchitale@...il.com>, Namhyung Kim <namhyung@...nel.org>,
 linux-riscv@...ts.infradead.org, Andrew Jones <ajones@...tanamicro.com>,
 Liang Kan <kan.liang@...ux.intel.com>
Subject: Re: [PATCH 05/11] rvtrace: Add trace encoder driver

On 10/1/25 23:07, Anup Patel wrote:
> From: Mayuresh Chitale <mchitale@...tanamicro.com>
> 
> Add initial implementation of RISC-V trace encoder driver. The encoder
> is defined in the RISC-V Trace Control Interface specification.
> 
> Co-developed-by: Anup Patel <apatel@...tanamicro.com>
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> Signed-off-by: Mayuresh Chitale <mchitale@...tanamicro.com>
> ---
>   drivers/hwtracing/rvtrace/Kconfig           |   7 ++
>   drivers/hwtracing/rvtrace/Makefile          |   1 +
>   drivers/hwtracing/rvtrace/rvtrace-encoder.c | 107 ++++++++++++++++++++
>   3 files changed, 115 insertions(+)
>   create mode 100644 drivers/hwtracing/rvtrace/rvtrace-encoder.c
> 
> diff --git a/drivers/hwtracing/rvtrace/Kconfig b/drivers/hwtracing/rvtrace/Kconfig
> index f8f6feea1953..ba35c05f3f54 100644
> --- a/drivers/hwtracing/rvtrace/Kconfig
> +++ b/drivers/hwtracing/rvtrace/Kconfig
> @@ -14,3 +14,10 @@ menuconfig RVTRACE
>   
>   	  To compile this driver as a module, choose M here: the module
>   	  will be called rvtrace.
> +
> +config RVTRACE_ENCODER
> +	tristate "RISC-V Trace Encoder driver"
> +	depends on RVTRACE
> +	default y
> +	help
> +	  This driver provides support for RISC-V Trace Encoder component.
> diff --git a/drivers/hwtracing/rvtrace/Makefile b/drivers/hwtracing/rvtrace/Makefile
> index 988525a379cf..f320693a1fc5 100644
> --- a/drivers/hwtracing/rvtrace/Makefile
> +++ b/drivers/hwtracing/rvtrace/Makefile
> @@ -2,3 +2,4 @@
>   
>   obj-$(CONFIG_RVTRACE) += rvtrace.o
>   rvtrace-y := rvtrace-core.o rvtrace-platform.o
> +obj-$(CONFIG_RVTRACE_ENCODER) += rvtrace-encoder.o
> diff --git a/drivers/hwtracing/rvtrace/rvtrace-encoder.c b/drivers/hwtracing/rvtrace/rvtrace-encoder.c
> new file mode 100644
> index 000000000000..45d1c5b12c51
> --- /dev/null
> +++ b/drivers/hwtracing/rvtrace/rvtrace-encoder.c
> @@ -0,0 +1,107 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2025 Ventana Micro Systems Inc.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/of_graph.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/rvtrace.h>
> +#include <linux/types.h>
> +
> +#define RVTRACE_COMPONENT_CTRL_ITRACE_MASK	0x1
> +#define RVTRACE_COMPONENT_CTRL_ITRACE_SHIFT	2
> +#define RVTRACE_COMPONENT_CTRL_INSTMODE_MASK	0x7
> +#define RVTRACE_COMPONENT_CTRL_INSTMODE_SHIFT	4
> +
> +static int rvtrace_encoder_start(struct rvtrace_component *comp)
> +{
> +	u32 val;
> +
> +	val = rvtrace_read32(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	val |= BIT(RVTRACE_COMPONENT_CTRL_ITRACE_SHIFT);
> +	rvtrace_write32(comp->pdata, val, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	return rvtrace_poll_bit(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET,
> +				RVTRACE_COMPONENT_CTRL_ITRACE_SHIFT, 1,
> +				comp->pdata->control_poll_timeout_usecs);
> +}
> +
> +static int rvtrace_encoder_stop(struct rvtrace_component *comp)
> +{
> +	u32 val;
> +
> +	val = rvtrace_read32(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	val &= ~BIT(RVTRACE_COMPONENT_CTRL_ITRACE_SHIFT);
> +	rvtrace_write32(comp->pdata, val, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	return rvtrace_poll_bit(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET,
> +				RVTRACE_COMPONENT_CTRL_ITRACE_SHIFT, 0,
> +				comp->pdata->control_poll_timeout_usecs);
> +}
> +
> +static void rvtrace_encoder_setmode(struct rvtrace_component *comp, u32 mode)
> +{
> +	u32 val;
> +
> +	val = rvtrace_read32(comp->pdata, RVTRACE_COMPONENT_CTRL_OFFSET);
> +	val |= (mode << RVTRACE_COMPONENT_CTRL_INSTMODE_SHIFT);
> +	rvtrace_write32(comp->pdata, val, RVTRACE_COMPONENT_CTRL_OFFSET);
> +}
> +
> +static int rvtrace_encoder_probe(struct rvtrace_component *comp)
> +{
> +	int ret;
> +
> +	rvtrace_encoder_setmode(comp, 0x6);
> +	ret = rvtrace_enable_component(comp);
> +	if (ret)
> +		return dev_err_probe(&comp->dev, ret, "failed to enable encoder.\n");
> +
> +	return 0;
> +}
Trace components needs proper probing before use. Refer to Control Interface
Spec: https://github.com/riscv-non-isa/tg-nexus-trace/releases/download/1.0_Ratified/RISC-V-Trace-Control-Interface.pdf
Chapter 5. This versioning applies to all components, e.g., sinks/funnels...
The driver should check the HW impl version with what it supports, and
rejects registering the component(s) if not supported. Chapter 5. has more
details.

> +
> +static void rvtrace_encoder_remove(struct rvtrace_component *comp)
> +{
> +	int ret;
> +
> +	ret = rvtrace_disable_component(comp);
> +	if (ret)
> +		dev_err(&comp->dev, "failed to disable encoder.\n");
> +}
> +
> +static struct rvtrace_component_id rvtrace_encoder_ids[] = {
> +	{ .type = RVTRACE_COMPONENT_TYPE_ENCODER,
> +	  .version = rvtrace_component_mkversion(1, 0), },
> +	{},
> +};
> +
> +static struct rvtrace_driver rvtrace_encoder_driver = {
> +	.id_table = rvtrace_encoder_ids,
> +	.start = rvtrace_encoder_start,
> +	.stop = rvtrace_encoder_stop,
> +	.probe = rvtrace_encoder_probe,
> +	.remove = rvtrace_encoder_remove,
> +	.driver = {
> +		.name = "rvtrace-encoder",
> +	},
> +};
> +
> +static int __init rvtrace_encoder_init(void)
> +{
> +	return rvtrace_register_driver(&rvtrace_encoder_driver);
> +}
> +
> +static void __exit rvtrace_encoder_exit(void)
> +{
> +	rvtrace_unregister_driver(&rvtrace_encoder_driver);
> +}
> +
> +module_init(rvtrace_encoder_init);
> +module_exit(rvtrace_encoder_exit);
> +
> +/* Module information */
> +MODULE_AUTHOR("Mayuresh Chitale <mchitale@...tanamicro.com>");
> +MODULE_DESCRIPTION("RISC-V Trace Encoder Driver");
> +MODULE_LICENSE("GPL");

Bo