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Message-ID: <CAFCwf11kg-ZvYjEKf=VrvgvM03QZp7GejFhJ=gbCp4up++4h2w@mail.gmail.com>
Date: Wed, 26 Oct 2022 09:38:13 +0300
From: Oded Gabbay <ogabbay@...nel.org>
To: Jiho Chu <jiho.chu@...sung.com>
Cc: David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
Jason Gunthorpe <jgg@...dia.com>,
John Hubbard <jhubbard@...dia.com>,
Alex Deucher <alexander.deucher@....com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
Daniel Stone <daniel@...ishbar.org>,
Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
Jeffrey Hugo <quic_jhugo@...cinc.com>,
Christoph Hellwig <hch@...radead.org>,
Kevin Hilman <khilman@...libre.com>,
Jagan Teki <jagan@...rulasolutions.com>,
Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
Maciej Kwapulinski <maciej.kwapulinski@...ux.intel.com>
Subject: Re: [RFC PATCH 3/3] drm: add dedicated minor for accelerator devices
On Tue, Oct 25, 2022 at 9:43 AM Jiho Chu <jiho.chu@...sung.com> wrote:
>
>
> On Sun, 23 Oct 2022 00:46:22 +0300
> Oded Gabbay <ogabbay@...nel.org> wrote:
>
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index b58ffb1433d6..c13701a8d4be 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -56,6 +56,9 @@ MODULE_LICENSE("GPL and additional rights");
> > static DEFINE_SPINLOCK(drm_minor_lock);
> > static struct idr drm_minors_idr;
> >
> > +static DEFINE_SPINLOCK(accel_minor_lock);
> > +static struct idr accel_minors_idr;
> > +
> > /*
> > * If the drm core fails to init for whatever reason,
> > * we should prevent any drivers from registering with it.
> > @@ -94,6 +97,8 @@ static struct drm_minor **drm_minor_get_slot(struct drm_device *dev,
> > return &dev->primary;
> > case DRM_MINOR_RENDER:
> > return &dev->render;
> > + case DRM_MINOR_ACCEL:
> > + return &dev->accel;
> > default:
> > BUG();
> > }
> > @@ -108,9 +113,15 @@ static void drm_minor_alloc_release(struct drm_device *dev, void *data)
> >
> > put_device(minor->kdev);
> >
> > - spin_lock_irqsave(&drm_minor_lock, flags);
> > - idr_remove(&drm_minors_idr, minor->index);
> > - spin_unlock_irqrestore(&drm_minor_lock, flags);
> > + if (minor->type == DRM_MINOR_ACCEL) {
> > + spin_lock_irqsave(&accel_minor_lock, flags);
> > + idr_remove(&accel_minors_idr, minor->index);
> > + spin_unlock_irqrestore(&accel_minor_lock, flags);
> > + } else {
> > + spin_lock_irqsave(&drm_minor_lock, flags);
> > + idr_remove(&drm_minors_idr, minor->index);
> > + spin_unlock_irqrestore(&drm_minor_lock, flags);
> > + }
> > }
> >
> > static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
> > @@ -127,13 +138,23 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
> > minor->dev = dev;
> >
> > idr_preload(GFP_KERNEL);
> > - spin_lock_irqsave(&drm_minor_lock, flags);
> > - r = idr_alloc(&drm_minors_idr,
> > - NULL,
> > - 64 * type,
> > - 64 * (type + 1),
> > - GFP_NOWAIT);
> > - spin_unlock_irqrestore(&drm_minor_lock, flags);
> > + if (type == DRM_MINOR_ACCEL) {
> > + spin_lock_irqsave(&accel_minor_lock, flags);
> > + r = idr_alloc(&accel_minors_idr,
> > + NULL,
> > + 64 * (type - DRM_MINOR_ACCEL),
> > + 64 * (type - DRM_MINOR_ACCEL + 1),
> > + GFP_NOWAIT);
> > + spin_unlock_irqrestore(&accel_minor_lock, flags);
> > + } else {
> > + spin_lock_irqsave(&drm_minor_lock, flags);
> > + r = idr_alloc(&drm_minors_idr,
> > + NULL,
> > + 64 * type,
> > + 64 * (type + 1),
> > + GFP_NOWAIT);
> > + spin_unlock_irqrestore(&drm_minor_lock, flags);
> > + }
>
> Hi,
> There are many functions which checks drm type and decides its behaviors. It's good to
> re-use exiting codes, but accel devices use totally different major/minor, and so it needs to be moved to
> /drvier/accel/ (maybe later..). How about seperating functions for alloc/release minor (accel_minor_alloc..)?
> also, for others which have drm type related codes.
My feeling was moving the minor code handling to a different file (in
addition to moving the major code handling) will cause too much
duplication.
My main theme is that an accel minor is another minor in drm, even if
a bit different. i.e. It uses the same drm_minor structure.
The driver declares he wants to use this minor using a drm driver feature flag.
imo, all of that indicates the code should be inside drm.
>
>
>
>
> > @@ -607,6 +652,14 @@ static int drm_dev_init(struct drm_device *dev,
> > /* no per-device feature limits by default */
> > dev->driver_features = ~0u;
> >
> > + if (drm_core_check_feature(dev, DRIVER_COMPUTE_ACCEL) &&
> > + (drm_core_check_feature(dev, DRIVER_RENDER) ||
> > + drm_core_check_feature(dev, DRIVER_MODESET))) {
> > +
> > + DRM_ERROR("DRM driver can't be both a compute acceleration and graphics driver\n");
> > + return -EINVAL;
> > + }
> > +
>
> It's fine for the device only for acceleration, but can't graphic devices have acceleration feature?
Of course they can :) In that case, and if they want to expose an
accel device char, they should write an accel driver and connect it to
their main graphics driver via auxiliary bus.
I could have added two flags - compute_accel, and compute_accel_only
(similar to a patch that was sent to add render only flag), but imo it
would make the code more convoluted. I prefer the clean separation and
using standard auxiliary bus.
Thanks,
Oded
>
>
> Thanks,
> Jiho Chu
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