[PATCHv2 03/16] Documentation: dt: add OMAP iommu bindings

On 02/26/2014 04:18 PM, Suman Anna wrote:

Hi Laurent,

On 02/26/2014 02:36 PM, Laurent Pinchart wrote:

quoted

Hi Suman,

On Wednesday 26 February 2014 14:23:03 Suman Anna wrote:

quoted

quoted

On Wednesday 26 February 2014 11:02:24 Suman Anna wrote:

quoted

On 02/25/2014 08:13 PM, Laurent Pinchart wrote:

quoted

On Tuesday 25 February 2014 17:02:35 Suman Anna wrote:

quoted

On 02/25/2014 03:26 PM, Laurent Pinchart wrote:

quoted

On Thursday 13 February 2014 12:15:34 Suman Anna wrote:

quoted

From: Florian Vaussard <redacted>

This patch adds the iommu bindings for all OMAP2+ SoCs. Apart from
the standard bindings used by OMAP peripherals, this patch uses a
'dma-window' (already used by Tegra SMMU) and adds two OMAP custom
bindings - 'ti,#tlb-entries' and 'ti,iommu-bus-err-back'.

Signed-off-by: Florian Vaussard <redacted>
[s-anna at ti.com: split bindings document, add dra7 and bus error
back]
Signed-off-by: Suman Anna <redacted>
---

  .../devicetree/bindings/iommu/ti,omap-iommu.txt    | 28
++++++++++++
  1 file changed, 28 insertions(+)
  create mode 100644
  Documentation/devicetree/bindings/iommu/ti,omap-iommu.txt

diff --git
a/Documentation/devicetree/bindings/iommu/ti,omap-iommu.txt
b/Documentation/devicetree/bindings/iommu/ti,omap-iommu.txt new
file
mode 100644
index 0000000..116492d

--- /dev/null
+++ b/Documentation/devicetree/bindings/iommu/ti,omap-iommu.txt

@@ -0,0 +1,28 @@
+OMAP2+ IOMMU
+
+Required properties:
+- compatible : Should be one of,
+        "ti,omap2-iommu" for OMAP2/OMAP3 IOMMU instances
+        "ti,omap4-iommu" for OMAP4/OMAP5 IOMMU instances
+        "ti,dra7-iommu" for DRA7xx IOMMU instances
+- ti,hwmods  : Name of the hwmod associated with the IOMMU

instance
+- reg        : Address space for the configuration registers
+- interrupts : Interrupt specifier for the IOMMU instance
+- dma-window : IOVA start address and length

Isn't the dma window more of a system configuration property than a
hardware property ? How do you expect it to be set?

We are setting it based on the addressable range for the MMU.

A quick look at the ISP and IVA IOMMUs in the OMAP3 shows that both
support the full 4GB VA space. Why do you need to restrict it ?

I should have rephrased it better when I said addressable range. While
the MMUs are capable of programming the full 4GB space, there are some
address ranges that are private from the processor view. This
window is
currently used to set the range for the omap-iovmm driver (which only
OMAP3 ISP is using atm), and there is no point in allowing the
omap-iovmm driver the full range when the processor could never
reach/access those addresses.

But the IOMMU VA space is from a device point of view, not from a CPU
point of view. Could you point me to where those private ranges are
documented, in order to understand the problem correctly ?

Yes, they are indeed from the device perspective. I meant DSP and/or IPU
by processor.

For example on OMAP3, you can refer to Table 2-9 in section 2.4.5 "DSP
Subsystem Memory Space Mapping" of the OMAP36xx TRM, and the external
addressable range starts from 0x11000000.

OK, so it looks more like a property of the IOMMU master than a
property of
the IOMMU itself. It would be better to express it as such, but I
wonder how
that could be done, and if it would be worth it in this case.

This property is currently solely used to configure the range for the
omap-iovmm module, which were supplied through platform data in the
non-DT case. I am wondering if the way to go here is to use
iommu_domain_set_attr() and use the domain geometry values.

The other option is to supply these as driver match data, and switching
the compatible strings to identify the MMU instance precisely.

regards
Suman

quoted

As not all masters (the OMAP3 ISP doesn't for instance) have restrictions
regarding the VA range they can address, should this property be at
least made
optional ?

quoted

quoted

quoted

quoted

quoted

We are reusing the existing defined property and it allows us to get
rid of the IOVA start and end addresses defined in the pre-DT OMAP
iommu platform data.

quoted

quoted

+Optional properties:
+- ti,#tlb-entries : Number of entries in the translation
look-aside
buffer. +                    Should be either 8 or 32 (default:
32)
+- ti,iommu-bus-err-back : Indicates the IOMMU instance supports
throwing
+                  back a bus error response on MMU faults.

Do these features vary per IOMMU instance or per IOMMU model ?
In the
latter case they could be inferred from the compatible string by
the
driver without requiring them to be explicit in DT (whether you
want
to do so is left to you though).

Well, these are fixed features given an IOMMU instance, like the
OMAP3
ISP is the only one that has 8 TLB entries, all the remaining
ones have
32, and the IPU iommu instances are the only ones that support
the bus
error response back. I have no preference to any particular way, and
sure the driver can infer these easily based on unique compatible
strings per subsystem per SoC. I just happened to go with defining
compatible strings per SoC, with the optional properties
differentiating the fixed behavior between different IOMMU
instances on
that SoC. This is where I was looking for some inputs/guidance
from the
DT bindings maintainers on what is the preferred method.

I think you've made the right choice. I wasn't sure whether those
parameters varied across IOMMU instances of compatible devices
(from a
compatible string point of view) or were constant. As they vary they
should be expressed in DT.

Yeah, I wasn't sure if these qualify as features (as per
Documentation/devicetree/bindings/ABI.txt section II.2).

regards
Suman

quoted

quoted

quoted

quoted

+Example:
+    /* OMAP3 ISP MMU */
+    mmu_isp: mmu at 480bd400 {
+        compatible = "ti,omap2-iommu";
+        reg = <0x480bd400 0x80>;
+        interrupts = <24>;
+        ti,hwmods = "mmu_isp";
+        ti,#tlb-entries = <8>;
+        dma-window = <0 0xfffff000>;
+    };