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Date: Tue, 27 Feb 2024 18:29:39 +0000
From: =?utf-8?Q?Adri=C3=A1n?= Larumbe <adrian.larumbe@collabora.com>
To: Steven Price <steven.price@arm.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>, 
	Rob Herring <robh@kernel.org>, Maarten Lankhorst <maarten.lankhorst@linux.intel.com>, 
	Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>, 
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>, 
	Jonathan Corbet <corbet@lwn.net>, kernel@collabora.com, linux-kernel@vger.kernel.org, 
	dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH] drm/panfrost: Replace fdinfo's profiling debugfs knob
 with sysfs
Message-ID: <eul246zgqqrweo6a3yacw4ukgoj3ixszlfdz42bgtzmivroyp4@2xevze2efqew>
References: <20240221161237.2478193-1-adrian.larumbe@collabora.com>
 <3769e867-64a8-4862-9791-da106eaa8501@arm.com>
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In-Reply-To: <3769e867-64a8-4862-9791-da106eaa8501@arm.com>

Hi Steve,

On 21.02.2024 16:52, Steven Price wrote:
> On 21/02/2024 16:12, Adrián Larumbe wrote:
> > Debugfs isn't always available in production builds that try to squeeze
> > every single byte out of the kernel image, but we still need a way to
> > toggle the timestamp and cycle counter registers so that jobs can be
> > profiled for fdinfo's drm engine and cycle calculations.
> > 
> > Drop the debugfs knob and replace it with a sysfs file that accomplishes
> > the same functionality, and document its ABI in a separate file.
> > 
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> > ---
> >  .../testing/sysfs-driver-panfrost-profiling   | 10 +++
> >  Documentation/gpu/panfrost.rst                |  9 +++
> >  drivers/gpu/drm/panfrost/Makefile             |  5 +-
> >  drivers/gpu/drm/panfrost/panfrost_debugfs.c   | 21 ------
> >  drivers/gpu/drm/panfrost/panfrost_debugfs.h   | 14 ----
> >  drivers/gpu/drm/panfrost/panfrost_device.h    |  5 +-
> >  drivers/gpu/drm/panfrost/panfrost_drv.c       | 14 ++--
> >  drivers/gpu/drm/panfrost/panfrost_job.c       |  2 +-
> >  drivers/gpu/drm/panfrost/panfrost_sysfs.c     | 74 +++++++++++++++++++
> >  drivers/gpu/drm/panfrost/panfrost_sysfs.h     | 15 ++++
> >  10 files changed, 124 insertions(+), 45 deletions(-)
> >  create mode 100644 Documentation/ABI/testing/sysfs-driver-panfrost-profiling
> >  delete mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.c
> >  delete mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.h
> >  create mode 100644 drivers/gpu/drm/panfrost/panfrost_sysfs.c
> >  create mode 100644 drivers/gpu/drm/panfrost/panfrost_sysfs.h
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-driver-panfrost-profiling b/Documentation/ABI/testing/sysfs-driver-panfrost-profiling
> > new file mode 100644
> > index 000000000000..ce54069714f3
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-driver-panfrost-profiling
> > @@ -0,0 +1,10 @@
> > +What:		/sys/bus/.../drivers/panfrost/.../drm/../profiling/status
> > +Date:		February 2024
> > +KernelVersion:	6.8.0
> > +Contact:	Adrian Larumbe <adrian.larumbe@collabora.com>
> > +Description:
> > +                Get/set drm fdinfo's engine and cycles profiling status.
> > +                Valid values are:
> > +		0: Disable fdinfo job profiling sources. This disables both the GPU's
> > +                timestamp and cycle counter registers.
> > +		1: Enable the above.
> 
> Minor point, but if we're going to eventually come up with a generic way
> of doing this, then we're going to have to think about backwards
> compatibility for this sysfs file. I would expect in this new world '0'
> would mean "default behaviour; off unless the new-fangled thing enables
> profiling" and '1' means "force on".
> 
> In which case perhaps wording like the below would be clearer:
> 
> 0: Don't enable fdinfo job profiling sources.
> 1: Enable fdinfo job profiling sources, this enables both the GPU's
>    timestamp and cycle counter registers.
> 
> Or am I being too picky over the wording ;)

I'm alright with this kind of wording, to keep things as generic as
possible. Initially I thought just mentioning 0 and 1 as potential toggle values
would be enough, and then every driver could describe their own profiling/status
sysfs knob in similar terms, depending on what profiling resouces they act upon.

> One other small issue below...
> 
> > diff --git a/Documentation/gpu/panfrost.rst b/Documentation/gpu/panfrost.rst
> > index b80e41f4b2c5..be4ac282ef63 100644
> > --- a/Documentation/gpu/panfrost.rst
> > +++ b/Documentation/gpu/panfrost.rst
> > @@ -38,3 +38,12 @@ the currently possible format options:
> >  
> >  Possible `drm-engine-` key names are: `fragment`, and  `vertex-tiler`.
> >  `drm-curfreq-` values convey the current operating frequency for that engine.
> > +
> > +Users must bear in mind that engine and cycle sampling are disabled by default,
> > +because of power saving concerns. `fdinfo` users and benchmark applications which
> > +query the fdinfo file must make sure to toggle the job profiling status of the
> > +driver by writing into the appropriate sysfs node::
> > +
> > +    echo <N> > /sys/bus/platform/drivers/panfrost/[a-f0-9]*.gpu/drm/card1/profiling
> > +
> > +Where `N` is either `0` or `1`, depending on the desired enablement status.
> > diff --git a/drivers/gpu/drm/panfrost/Makefile b/drivers/gpu/drm/panfrost/Makefile
> > index 2c01c1e7523e..6e718595d8a6 100644
> > --- a/drivers/gpu/drm/panfrost/Makefile
> > +++ b/drivers/gpu/drm/panfrost/Makefile
> > @@ -10,8 +10,7 @@ panfrost-y := \
> >  	panfrost_job.o \
> >  	panfrost_mmu.o \
> >  	panfrost_perfcnt.o \
> > -	panfrost_dump.o
> > -
> > -panfrost-$(CONFIG_DEBUG_FS) += panfrost_debugfs.o
> > +	panfrost_dump.o \
> > +	panfrost_sysfs.o
> >  
> >  obj-$(CONFIG_DRM_PANFROST) += panfrost.o
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_debugfs.c b/drivers/gpu/drm/panfrost/panfrost_debugfs.c
> > deleted file mode 100644
> > index 72d4286a6bf7..000000000000
> > --- a/drivers/gpu/drm/panfrost/panfrost_debugfs.c
> > +++ /dev/null
> > @@ -1,21 +0,0 @@
> > -// SPDX-License-Identifier: GPL-2.0
> > -/* Copyright 2023 Collabora ltd. */
> > -/* Copyright 2023 Amazon.com, Inc. or its affiliates. */
> > -
> > -#include <linux/debugfs.h>
> > -#include <linux/platform_device.h>
> > -#include <drm/drm_debugfs.h>
> > -#include <drm/drm_file.h>
> > -#include <drm/panfrost_drm.h>
> > -
> > -#include "panfrost_device.h"
> > -#include "panfrost_gpu.h"
> > -#include "panfrost_debugfs.h"
> > -
> > -void panfrost_debugfs_init(struct drm_minor *minor)
> > -{
> > -	struct drm_device *dev = minor->dev;
> > -	struct panfrost_device *pfdev = platform_get_drvdata(to_platform_device(dev->dev));
> > -
> > -	debugfs_create_atomic_t("profile", 0600, minor->debugfs_root, &pfdev->profile_mode);
> > -}
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_debugfs.h b/drivers/gpu/drm/panfrost/panfrost_debugfs.h
> > deleted file mode 100644
> > index c5af5f35877f..000000000000
> > --- a/drivers/gpu/drm/panfrost/panfrost_debugfs.h
> > +++ /dev/null
> > @@ -1,14 +0,0 @@
> > -/* SPDX-License-Identifier: GPL-2.0 */
> > -/*
> > - * Copyright 2023 Collabora ltd.
> > - * Copyright 2023 Amazon.com, Inc. or its affiliates.
> > - */
> > -
> > -#ifndef PANFROST_DEBUGFS_H
> > -#define PANFROST_DEBUGFS_H
> > -
> > -#ifdef CONFIG_DEBUG_FS
> > -void panfrost_debugfs_init(struct drm_minor *minor);
> > -#endif
> > -
> > -#endif  /* PANFROST_DEBUGFS_H */
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> > index 62f7e3527385..56c8e5551335 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> > @@ -130,7 +130,10 @@ struct panfrost_device {
> >  	struct list_head scheduled_jobs;
> >  
> >  	struct panfrost_perfcnt *perfcnt;
> > -	atomic_t profile_mode;
> > +	struct kobj_profiling {
> > +		struct kobject base;
> > +		atomic_t profile_mode;
> > +	} profiling;
> >  
> >  	struct mutex sched_lock;
> >  
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > index a926d71e8131..6db1ea453514 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > @@ -20,7 +20,7 @@
> >  #include "panfrost_job.h"
> >  #include "panfrost_gpu.h"
> >  #include "panfrost_perfcnt.h"
> > -#include "panfrost_debugfs.h"
> > +#include "panfrost_sysfs.h"
> >  
> >  static bool unstable_ioctls;
> >  module_param_unsafe(unstable_ioctls, bool, 0600);
> > @@ -600,10 +600,6 @@ static const struct drm_driver panfrost_drm_driver = {
> >  
> >  	.gem_create_object	= panfrost_gem_create_object,
> >  	.gem_prime_import_sg_table = panfrost_gem_prime_import_sg_table,
> > -
> > -#ifdef CONFIG_DEBUG_FS
> > -	.debugfs_init		= panfrost_debugfs_init,
> > -#endif
> >  };
> >  
> >  static int panfrost_probe(struct platform_device *pdev)
> > @@ -663,8 +659,14 @@ static int panfrost_probe(struct platform_device *pdev)
> >  	if (err)
> >  		goto err_out2;
> >  
> > +	err = panfrost_sysfs_init(pfdev);
> > +	if (err)
> > +		goto err_out3;
> > +
> >  	return 0;
> >  
> > +err_out3:
> > +	panfrost_gem_shrinker_cleanup(ddev);
> >  err_out2:
> >  	drm_dev_unregister(ddev);
> >  err_out1:
> > @@ -681,6 +683,8 @@ static void panfrost_remove(struct platform_device *pdev)
> >  	struct panfrost_device *pfdev = platform_get_drvdata(pdev);
> >  	struct drm_device *ddev = pfdev->ddev;
> >  
> > +	panfrost_sysfs_cleanup(pfdev);
> > +
> >  	drm_dev_unregister(ddev);
> >  	panfrost_gem_shrinker_cleanup(ddev);
> >  
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> > index 0c2dbf6ef2a5..49413dfda2ea 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> > @@ -243,7 +243,7 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
> >  	subslot = panfrost_enqueue_job(pfdev, js, job);
> >  	/* Don't queue the job if a reset is in progress */
> >  	if (!atomic_read(&pfdev->reset.pending)) {
> > -		if (atomic_read(&pfdev->profile_mode)) {
> > +		if (atomic_read(&pfdev->profiling.profile_mode)) {
> >  			panfrost_cycle_counter_get(pfdev);
> >  			job->is_profiled = true;
> >  			job->start_time = ktime_get();
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_sysfs.c b/drivers/gpu/drm/panfrost/panfrost_sysfs.c
> > new file mode 100644
> > index 000000000000..072d3bf349d2
> > --- /dev/null
> > +++ b/drivers/gpu/drm/panfrost/panfrost_sysfs.c
> > @@ -0,0 +1,74 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright 2023 Collabora ltd. */
> > +/* Copyright 2023 Amazon.com, Inc. or its affiliates. */
> > +
> > +#include <linux/platform_device.h>
> > +#include <drm/drm_file.h>
> > +#include <drm/panfrost_drm.h>
> > +
> > +#include "panfrost_device.h"
> > +#include "panfrost_gpu.h"
> > +#include "panfrost_sysfs.h"
> > +
> > +static ssize_t
> > +profiling_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
> > +{
> > +	atomic_t *profile_mode =
> > +		&container_of(kobj, struct {
> > +			struct kobject base;
> > +			atomic_t profile_mode; },
> > +			base)->profile_mode;
> 
> Yuck! ;) That's likely to catch people out if they modify the struct in
> the header file.

Sorry about this abomination. I think it slipped through the cracks after a
first patch draft in which I didn't want to make the kobject-holding structure a
global declaration.

> Why not "struct kobj_profiling" rather than that inline struct. I'd also
> argue that kobj_profiling isn't a great name and I'd suggest something
> with 'panfrost' in the name. Or you could just use the parent struct
> panfrost_device and not bother naming this sub-struct, e.g.
> 
> &container_of(kobj, struct panfrost_device,
>               profiling.base)->profiling.profile_mode;

This is a much better way of doing things than mine. Thanks!

> Thanks,
> Steve
> 
> > +
> > +	return sysfs_emit(buf, "%d\n", atomic_read(profile_mode));
> > +}
> > +
> > +static ssize_t
> > +profiling_store(struct kobject *kobj, struct kobj_attribute *attr,
> > +	       const char *buf, size_t count)
> > +{
> > +	atomic_t *profile_mode =
> > +		&container_of(kobj, struct {
> > +			struct kobject base;
> > +			atomic_t profile_mode; },
> > +			base)->profile_mode;
> > +	int err, value;
> > +
> > +	err = kstrtoint(buf, 0, &value);
> > +	if (err)
> > +		return err;
> > +
> > +	atomic_set(profile_mode, !!value);
> > +
> > +	return count;
> > +}
> > +
> > +static const struct kobj_attribute profiling_status =
> > +__ATTR(status, 0644, profiling_show, profiling_store);
> > +
> > +static const struct kobj_type kobj_profile_type = {
> > +	.sysfs_ops = &kobj_sysfs_ops,
> > +};
> > +
> > +int panfrost_sysfs_init(struct panfrost_device *pfdev)
> > +{
> > +	struct device *kdev = pfdev->ddev->primary->kdev;
> > +	int err;
> > +
> > +	kobject_init(&pfdev->profiling.base, &kobj_profile_type);
> > +
> > +	err = kobject_add(&pfdev->profiling.base, &kdev->kobj, "%s", "profiling");
> > +	if (err)
> > +		return err;
> > +
> > +	err = sysfs_create_file(&pfdev->profiling.base, &profiling_status.attr);
> > +	if (err)
> > +		kobject_del(&pfdev->profiling.base);
> > +
> > +	return err;
> > +}
> > +
> > +void panfrost_sysfs_cleanup(struct panfrost_device *pfdev)
> > +{
> > +	sysfs_remove_file(&pfdev->profiling.base, &profiling_status.attr);
> > +	kobject_del(&pfdev->profiling.base);
> > +}
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_sysfs.h b/drivers/gpu/drm/panfrost/panfrost_sysfs.h
> > new file mode 100644
> > index 000000000000..5fc9c8c1091a
> > --- /dev/null
> > +++ b/drivers/gpu/drm/panfrost/panfrost_sysfs.h
> > @@ -0,0 +1,15 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright 2023 Collabora ltd.
> > + * Copyright 2023 Amazon.com, Inc. or its affiliates.
> > + */
> > +
> > +#ifndef PANFROST_SYSFS_H
> > +#define PANFROST_SYSFS_H
> > +
> > +struct panfrost_device;
> > +
> > +int panfrost_sysfs_init(struct panfrost_device *pfdev);
> > +void panfrost_sysfs_cleanup(struct panfrost_device *pfdev);
> > +
> > +#endif  /* PANFROST_SYSFS_H */