On 19/02/2020 2:29 pm, Roger Quadros wrote:
Rob,
On 18/02/2020 19:22, Rob Herring wrote:
On Tue, Feb 18, 2020 at 2:28 AM Roger Quadros <rogerq@xxxxxx> wrote:
Chrishtoph,
The branch works fine for SATA on DRA7 with CONFIG_LPAE once I
have the below DT fix.
Do you intend to send these fixes to -stable?
------------------------- arch/arm/boot/dts/dra7.dtsi
-------------------------
index d78b684e7fca..853ecf3cfb37 100644
@@ -645,6 +645,8 @@
sata: sata@4a141100 {
compatible = "snps,dwc-ahci";
reg = <0x4a140000 0x1100>, <0x4a141100 0x7>;
+ #size-cells = <2>;
+ dma-ranges = <0x00000000 0x00000000 0x1
0x00000000>;
dma-ranges should be in the parent (bus) node, not the device node.
I didn't understand why.
There are many devices on the parent bus node and all devices might not
have the 32-bit DMA limit
the SATA controller has.
SATA controller is the bus master and the ATA devices are children of
the SATA controller.
But SATA is not a memory-mapped bus - in the context of MMIO, the AHCI
is the bus-master device, not a bridge or level of interconnect. The
DeviceTree spec[1] clearly defines dma-ranges as an address translation
between a "parent bus" and a "child bus".
If in the worst case this address-limited interconnect really only
exists between the AHCI's master interface and everything else in the
system, then you'll have to describe it explicitly to meet DT's
expectation of a "bus" (e.g. [2]). Yes, it's a bit clunky, but any
scheme has its edge cases.
From Documentation/devicetree/booting-without-of.txt
* DMA Bus master
Optional property:
- dma-ranges: <prop-encoded-array> encoded as arbitrary number of
triplets of
(child-bus-address, parent-bus-address, length). Each triplet
specified
describes a contiguous DMA address range.
The dma-ranges property is used to describe the direct memory
access (DMA)
structure of a memory-mapped bus whose device tree parent can
be accessed
from DMA operations originating from the bus. It provides a
means of
defining a mapping or translation between the physical address
space of
the bus and the physical address space of the parent of the bus.
(for more information see the Devicetree Specification)
* DMA Bus child
Optional property:
- dma-ranges: <empty> value. if present - It means that DMA addresses
translation has to be enabled for this device.
Disregarding that this was apparently never in ePAPR, so not
grandfathered in to DTSpec, and effectively nobody ever has actually
followed it (oh, if only...), note "<empty>" - that still doesn't imply
that a *non-empty* dma-ranges would be valid on device nodes.
Robin.
[1] https://www.devicetree.org/specifications/
[2]
https://lore.kernel.org/lkml/20181010120737.30300-20-laurentiu.tudor@xxxxxxx/
