From: Jason Gunthorpe <jgg@nvidia.com>
To: Oded Gabbay <ogabbay@kernel.org>
Cc: dri-devel@lists.freedesktop.org,
Maciej Kwapulinski <maciej.kwapulinski@linux.intel.com>,
Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>,
Kevin Hilman <khilman@baylibre.com>,
Christoph Hellwig <hch@infradead.org>,
Jagan Teki <jagan@amarulasolutions.com>,
John Hubbard <jhubbard@nvidia.com>,
Jeffrey Hugo <quic_jhugo@quicinc.com>,
Arnd Bergmann <arnd@arndb.de>, Jiho Chu <jiho.chu@samsung.com>,
Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>,
Yuji Ishikawa <yuji2.ishikawa@toshiba.co.jp>,
Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>,
linux-kernel@vger.kernel.org,
Thomas Zimmermann <tzimmermann@suse.de>,
Alex Deucher <alexander.deucher@amd.com>
Subject: Re: [RFC PATCH v3 0/3] new subsystem for compute accelerator devices
Date: Mon, 7 Nov 2022 12:20:08 -0400 [thread overview]
Message-ID: <Y2kwOO9GOUF9DsJj@nvidia.com> (raw)
In-Reply-To: <20221106210225.2065371-1-ogabbay@kernel.org>
On Sun, Nov 06, 2022 at 11:02:22PM +0200, Oded Gabbay wrote:
> Another important change is that I have reverted back to use IDR for minor
> handling instead of xarray. This is because I have found that xarray doesn't
> handle well the scenario where you allocate a NULL entry and then exchange it
> with a real pointer. It appears xarray still considers that entry a "zero"
> entry. This is unfortunate because DRM works that way (first allocates a NULL
> entry and then replaces the entry with a real pointer).
This is what XA_ZERO_ENTRY is for.
Some APIs, like xa_alloc automatically promote NULL to XA_ZERO_ENTRY,
others require it to be explicit.
If you use the usual pattern of xa_alloc(NULL), xa_store(!NULL) then
you should be fine, as far as I know. So long as the xarray was tagged
as allocating.
Jason
WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg@nvidia.com>
To: Oded Gabbay <ogabbay@kernel.org>
Cc: David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
John Hubbard <jhubbard@nvidia.com>,
Alex Deucher <alexander.deucher@amd.com>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <mripard@kernel.org>,
Thomas Zimmermann <tzimmermann@suse.de>,
Yuji Ishikawa <yuji2.ishikawa@toshiba.co.jp>,
Jiho Chu <jiho.chu@samsung.com>,
Daniel Stone <daniel@fooishbar.org>,
Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
Jeffrey Hugo <quic_jhugo@quicinc.com>,
Christoph Hellwig <hch@infradead.org>,
Kevin Hilman <khilman@baylibre.com>,
Jagan Teki <jagan@amarulasolutions.com>,
Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>,
Maciej Kwapulinski <maciej.kwapulinski@linux.intel.com>,
Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [RFC PATCH v3 0/3] new subsystem for compute accelerator devices
Date: Mon, 7 Nov 2022 12:20:08 -0400 [thread overview]
Message-ID: <Y2kwOO9GOUF9DsJj@nvidia.com> (raw)
In-Reply-To: <20221106210225.2065371-1-ogabbay@kernel.org>
On Sun, Nov 06, 2022 at 11:02:22PM +0200, Oded Gabbay wrote:
> Another important change is that I have reverted back to use IDR for minor
> handling instead of xarray. This is because I have found that xarray doesn't
> handle well the scenario where you allocate a NULL entry and then exchange it
> with a real pointer. It appears xarray still considers that entry a "zero"
> entry. This is unfortunate because DRM works that way (first allocates a NULL
> entry and then replaces the entry with a real pointer).
This is what XA_ZERO_ENTRY is for.
Some APIs, like xa_alloc automatically promote NULL to XA_ZERO_ENTRY,
others require it to be explicit.
If you use the usual pattern of xa_alloc(NULL), xa_store(!NULL) then
you should be fine, as far as I know. So long as the xarray was tagged
as allocating.
Jason
next prev parent reply other threads:[~2022-11-07 16:20 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-06 21:02 [RFC PATCH v3 0/3] new subsystem for compute accelerator devices Oded Gabbay
2022-11-06 21:02 ` Oded Gabbay
2022-11-06 21:02 ` [RFC PATCH v3 1/3] drivers/accel: define kconfig and register a new major Oded Gabbay
2022-11-06 21:02 ` Oded Gabbay
2022-11-07 16:12 ` Jeffrey Hugo
2022-11-07 16:12 ` Jeffrey Hugo
2022-11-07 21:05 ` Oded Gabbay
2022-11-07 21:05 ` Oded Gabbay
2022-11-08 12:46 ` Stanislaw Gruszka
2022-11-08 12:46 ` Stanislaw Gruszka
2022-11-08 12:48 ` Oded Gabbay
2022-11-08 12:48 ` Oded Gabbay
2022-11-06 21:02 ` [RFC PATCH v3 2/3] accel: add dedicated minor for accelerator devices Oded Gabbay
2022-11-06 21:02 ` Oded Gabbay
2022-11-07 16:20 ` Jeffrey Hugo
2022-11-07 16:20 ` Jeffrey Hugo
2022-11-07 21:06 ` Oded Gabbay
2022-11-07 21:06 ` Oded Gabbay
2022-11-08 13:13 ` Tvrtko Ursulin
2022-11-08 13:13 ` Tvrtko Ursulin
2022-11-08 16:14 ` Oded Gabbay
2022-11-08 16:14 ` Oded Gabbay
2022-11-06 21:02 ` [RFC PATCH v3 3/3] drm: initialize accel framework Oded Gabbay
2022-11-06 21:02 ` Oded Gabbay
2022-11-07 16:24 ` Jeffrey Hugo
2022-11-07 16:24 ` Jeffrey Hugo
2022-11-07 21:04 ` Oded Gabbay
2022-11-07 21:04 ` Oded Gabbay
2022-11-07 16:07 ` [RFC PATCH v3 0/3] new subsystem for compute accelerator devices Jeffrey Hugo
2022-11-07 16:07 ` Jeffrey Hugo
2022-11-07 16:21 ` Matthew Wilcox
2022-11-07 16:21 ` Matthew Wilcox
2022-11-07 16:20 ` Jason Gunthorpe [this message]
2022-11-07 16:20 ` Jason Gunthorpe
2022-11-11 22:03 ` Christopher Friedt
2022-11-11 22:03 ` Christopher Friedt
2022-11-13 15:05 ` Oded Gabbay
2022-11-13 15:05 ` Oded Gabbay
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