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Tue, 25 Oct 2022 13:26:58 +0000 Received: from DM4PR11MB5373.namprd11.prod.outlook.com ([fe80::f131:2364:3638:6505]) by DM4PR11MB5373.namprd11.prod.outlook.com ([fe80::f131:2364:3638:6505%6]) with mapi id 15.20.5746.028; Tue, 25 Oct 2022 13:26:58 +0000 Date: Tue, 25 Oct 2022 15:26:54 +0200 From: =?utf-8?Q?Micha=C5=82?= Winiarski To: Oded Gabbay CC: Jeffrey Hugo , David Airlie , Daniel Vetter , Arnd Bergmann , "Greg Kroah-Hartman" , , , Jason Gunthorpe , "John Hubbard" , Alex Deucher , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Yuji Ishikawa , Jiho Chu , Daniel Stone , Tvrtko Ursulin , Christoph Hellwig , Kevin Hilman , Jagan Teki , Jacek Lawrynowicz , Maciej Kwapulinski Subject: Re: [RFC PATCH 3/3] drm: add dedicated minor for accelerator devices Message-ID: <20221025132654.fcbw7xvl7pu3yp6c@nostramo> References: <20221022214622.18042-1-ogabbay@kernel.org> <20221022214622.18042-4-ogabbay@kernel.org> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: LO4P123CA0597.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:295::14) To DM4PR11MB5373.namprd11.prod.outlook.com (2603:10b6:5:394::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB5373:EE_|SA2PR11MB5004:EE_ X-MS-Office365-Filtering-Correlation-Id: 9e2ac2c3-510b-46d3-27bc-08dab68c96ff X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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In addition, they are represented in /dev with new, dedicated > > > device char names: /dev/accel/accel*. This is done to make sure any > > > user-space software that tries to open a graphic card won't open > > > the accelerator device by mistake. > > > > > > The above implies that the minor numbering should be separated from > > > the rest of the drm devices. However, to avoid code duplication, we > > > want the drm_minor structure to be able to represent the accelerator > > > device. > > > > > > To achieve this, we add a new drm_minor* to drm_device that represents > > > the accelerator device. This pointer is initialized for drivers that > > > declare they handle compute accelerator, using a new driver feature > > > flag called DRIVER_COMPUTE_ACCEL. It is important to note that this > > > driver feature is mutually exclusive with DRIVER_RENDER. Devices that > > > want to expose both graphics and compute device char files should be > > > handled by two drivers that are connected using the auxiliary bus > > > framework. > > > > > > In addition, we define a different idr to handle the accelerators > > > minors. This is done to make the minor's index be identical to the > > > device index in /dev/. In most places, this is hidden inside the drm > > > core functions except when calling drm_minor_acquire(), where I had to > > > add an extra parameter to specify the idr to use (because the > > > accelerators minors index and the drm primary minor index both begin > > > at 0). > > > > > > Signed-off-by: Oded Gabbay > > > --- > > > drivers/gpu/drm/drm_drv.c | 171 +++++++++++++++++++++++++-------- > > > drivers/gpu/drm/drm_file.c | 69 +++++++++---- > > > drivers/gpu/drm/drm_internal.h | 2 +- > > > drivers/gpu/drm/drm_sysfs.c | 29 ++++-- > > > include/drm/drm_device.h | 3 + > > > include/drm/drm_drv.h | 8 ++ > > > include/drm/drm_file.h | 21 +++- > > > 7 files changed, 235 insertions(+), 68 deletions(-) > > > > Can we please add something to Documentation? I know this leverages DRM > > a lot, but I believe that a new subsystem should not be introduced > > without documentation. A lot of the info in the commit message is very > > good, but should not be buried in the git log. > > > > Besides, imagine this has been in mainline for N years, and someone > > completely new to the kernel wants to write an accel driver. They > > should be able to get started with something from Documentation that > > at-least gives that person some insight into what to grep the code for. > Agreed. The only reason I haven't done it at this stage was because I > wanted to get an initial reaction to the code itself, see if the > direction is accepted. > I didn't want to write documentation and then completely re-write it. > So I will do it for the next patch-set, once I collect everyone's > feedback and I see there is a majority agreement. > > > > > > > > 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; > > > > IDR is deprecated. XArray is the preferred mechanism. > > Yes, there already is IDR here, but I believe we should not be adding > > new uses. Maybe at some point, the current IDR will be converted. Also > > with XArray, I think you don't need the spinlock since XArray has > > internal locking already. > ok, I wasn't aware. I don't have any problem replacing the idr to xarray. The conversion is sitting on the mailinglist for a while now (unfortunately, without much interest). Perhaps you could help with reviewing it? https://lore.kernel.org/dri-devel/20220911211443.581481-2-michal.winiarski@intel.com/ -Michał > > Thanks, > Oded >