Hello,
On 2014-09-01 11:38, Arnd Bergmann wrote:
On Monday 01 September 2014 09:53:29 Marek Szyprowski wrote:
On 2014-09-01 09:07, Thierry Reding wrote:
On Mon, Sep 01, 2014 at 07:22:32AM +0200, Marek Szyprowski wrote:
Hi Greg,
On 2014-08-05 12:47, Marek Szyprowski wrote:
This patch adds a new flags for device drivers. This flag instructs
kernel that the device driver does it own management of IOMMU assisted
IO address space translations, so no default dma-mapping structures
should be initialized.
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
include/linux/device.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/include/linux/device.h b/include/linux/device.h
index 5f4ff02..2e62371 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -253,6 +253,8 @@ struct device_driver {
/* disables bind/unbind via sysfs */
#define DRIVER_SUPPRESS_BIND_ATTRS (1 << 0)
+/* driver uses own methods to manage IO address space */
+#define DRIVER_HAS_OWN_IOMMU_MANAGER (1 << 1)
extern int __must_check driver_register(struct device_driver *drv);
extern void driver_unregister(struct device_driver *drv);
Could you comment if the approach of using flags in the struct driver
could be accepted? I've converted suppress_bind_attrs entry to flags to
avoid extending the structure, please see patch "[PATCH 05/29] drivers:
convert suppress_bind_attrs parameter into flags".
Is this really necessary? What I did as part of an RFC series for Tegra
IOMMU support is keep this knowledge within the IOMMU driver rather than
export it to the driver core.i
The problem with embedding the list of drivers that you would need to update
it everytime when you modify or extend iommu support in the other drivers.
I've tried also other approach, like adding respective notifiers to
individual
drivers to initialize custom iommu support (or disable default iommu
mapping)
before iommu driver gets initialized, but such solution is in my opinion too
complex and hard to understand if one is not familiar will all this stuff.
All in all it turned out that the simplest and most generic way is to simply
add the flag to the driver core. Flags might be also used in the future
to model other kinds of dependencies between device drivers and/or driver
core.
I don't get it yet. I would expect that a driver doing its own management
of the iommu gets to use the linux/iommu.h interfaces, while a driver
using the default iommu setup uses linux/dma-mapping.h.
You are right.
Who do you think needs to set this flag, and who needs to read it?
In the proposed solution Exynos IOMMU driver creates a separate IO
address space
for every client device in a system and binds it to the default
dma-mapping space
for the given device. When drivers are doing its own management of IO
address
space, instead of relying on what is available by default with dma-mapping
interface, this will require releasing of the previously created default
structures and resources. So this flag is set by the driver doing its own
management of io address space. The flags is then checked by Exynos
IOMMU driver
to avoid creating the default dma-mapping address space for devices
which driver
does its own management.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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