From: Rob Clark <robdclark@gmail.com>
To: Joerg Roedel <joro@8bytes.org>
Cc: "list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
Joerg Roedel <joro@8bytes.org>,"
<iommu@lists.linux-foundation.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
aarch64-laptops@lists.linaro.org,
Jordan Crouse <jcrouse@codeaurora.org>,
Rob Clark <robdclark@chromium.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Ulf Hansson <ulf.hansson@linaro.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Heikki Krogerus <heikki.krogerus@linux.intel.com>,
Vivek Gautam <vivek.gautam@codeaurora.org>,
Bartosz Golaszewski <brgl@bgdev.pl>,
Joe Perches <joe@perches.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>
Subject: Re: [PATCH 1/2] iommu: add support for drivers that manage iommu explicitly
Date: Thu, 4 Jul 2019 06:51:23 -0700 [thread overview]
Message-ID: <CAF6AEGtjMqoFprY+r6zwUxxpm9iFfN-n-uNad3w9vxOCcTrQJA@mail.gmail.com> (raw)
In-Reply-To: <20190704082001.GD6546@8bytes.org>
On Thu, Jul 4, 2019 at 1:20 AM Joerg Roedel <joro@8bytes.org> wrote:
>
> Hi Rob,
>
> On Tue, Jul 02, 2019 at 01:26:18PM -0700, Rob Clark wrote:
> > 1) In some cases the bootloader takes the iommu out of bypass and
> > enables the display. This is in particular a problem on the aarch64
> > laptops that exist these days, and modern snapdragon android devices.
> > (Older devices also enabled the display in bootloader but did not
> > take the iommu out of bypass.) Attaching a DMA or IDENTITY domain
> > while scanout is active, before the driver has a chance to intervene,
> > makes things go *boom*
>
> Just to make sure I get this right: The bootloader inializes the SMMU
> and creates non-identity mappings for the GPU? And when the SMMU driver
> in Linux takes over this breaks display output.
correct
> > + /*
> > + * If driver is going to manage iommu directly, then avoid
> > + * attaching any non driver managed domain. There could
> > + * be already active dma underway (ie. scanout in case of
> > + * bootloader enabled display), and interfering with that
> > + * will make things go *boom*
> > + */
> > + if ((domain->type != IOMMU_DOMAIN_UNMANAGED) &&
> > + dev->driver && dev->driver->driver_manages_iommu)
> > + return 0;
> > +
>
> When the default domain is attached, there is usually no driver attached
> yet. I think this needs to be communicated by the firmware to Linux and
> the code should check against that.
At least for the OF case, it happens in the of_dma_configure() which
happens from really_probe(), so there is normally a driver. There are
a few exceptional cases, where drivers call of_dma_configure() on
their own sub-device without a driver attached (hence the need to
check if dev->driver is NULL).
I'm also interested in the ACPI case eventually... the aarch64
"windows" laptops do have ACPI. But for now we are booting with DT
since there is quite a lot of work before we get to point of using
ACPI. (In particular, under windows, device power management is done
thru a Platform Extension Plugin (PEP), but so far linux has no such
mechanism.)
We really don't have control of the firmware. But when arm-smmu is
probed it can read back the hw state and figure out what is going on
(with an RFC series[1] from Bjorn which was posted earlier), so we
don't really need to depend on the firmware.
> > - bool suppress_bind_attrs; /* disables bind/unbind via sysfs */
> > + bool suppress_bind_attrs:1; /* disables bind/unbind via sysfs */
> > + bool driver_manages_iommu:1; /* driver manages IOMMU explicitly */
>
> How does this field get set?
It is set in the driver in the second patch[2] in this series.
BR,
-R
[1] https://www.spinics.net/lists/arm-kernel/msg732246.html
[2] https://patchwork.freedesktop.org/patch/315291/
next prev parent reply other threads:[~2019-07-04 13:51 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-02 20:26 [PATCH 0/2] iommu: handle drivers that manage iommu directly Rob Clark
2019-07-02 20:26 ` [PATCH 1/2] iommu: add support for drivers that manage iommu explicitly Rob Clark
2019-07-03 12:42 ` Robin Murphy
2019-07-03 14:18 ` Rob Clark
2019-07-04 8:20 ` Joerg Roedel
2019-07-04 13:51 ` Rob Clark [this message]
2019-07-10 18:28 ` [PATCH v2] " Rob Clark
2019-07-22 14:28 ` Joerg Roedel
2019-07-22 15:41 ` Rob Clark
2019-07-22 15:48 ` Joerg Roedel
2019-07-22 16:23 ` Rob Clark
2019-07-23 15:38 ` Will Deacon
2019-07-23 17:40 ` Rob Clark
2019-07-24 10:51 ` Will Deacon
2019-07-24 16:11 ` Rob Clark
2019-07-02 20:26 ` [PATCH 2/2] drm/msm: mark devices where iommu is managed by driver Rob Clark
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