Re: [PATCH 3/3] dt-bindings: Document the STM32 USB OTG DWC2 core binding

On Wed, Jun 29, 2016 at 03:56:23PM -0300, Bruno Herrera wrote:

On Tue, Jun 28, 2016 at 5:54 PM, Rob Herring [off-list ref] wrote:

quoted

On Fri, Jun 24, 2016 at 03:51:18PM -0300, Bruno Herrera wrote:

quoted

On Fri, Jun 24, 2016 at 12:41 PM, Rob Herring [off-list ref] wrote:

quoted

On Tue, Jun 21, 2016 at 11:25:49PM -0300, Bruno Herrera wrote:

quoted

Signed-off-by: Bruno Herrera <redacted>
---
 Documentation/devicetree/bindings/usb/dwc2.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Documentation/devicetree/bindings/usb/dwc2.txt b/Documentation/devicetree/bindings/usb/dwc2.txt
index 20a68bf..79e5370 100644
--- a/Documentation/devicetree/bindings/usb/dwc2.txt
+++ b/Documentation/devicetree/bindings/usb/dwc2.txt

@@ -11,6 +11,7 @@ Required properties:
   - "lantiq,arx100-usb": The DWC2 USB controller instance in Lantiq ARX SoCs;
   - "lantiq,xrx200-usb": The DWC2 USB controller instance in Lantiq XRX SoCs;
   - snps,dwc2: A generic DWC2 USB controller with default parameters.
+  - st,stm32-fsotg: The DWC2 USB controller instance in STM32F4 SoCs in FS mode;

This should go above snps,dwc2.

Ok, tks!

quoted

What determines FS mode vs. HS?

Its more HW design decision.
STM32F429/439/469 has two OTG controllers, one that is FS (internal
phy) and other that is HS (but can also work in FS mode with
internal/external phy)
This bind work with both cores FS and HS working with the internal PHY.

I tested the following configurations:
1 - STM32F429I-DISCOv1 board (OTG HS working in FS mode internal PHY)
2 - STM32F469I-DISCO board (OTG FS)

I did not tested OTG HS core working in FS mode with external PHY (I2C).

You shouldn't be setting the compatible string based on which mode you
want. So for the HS block, you need a different compatible string than
the FS block and set the speed in another way (not sure if we have a
standard way). Or perhaps the phy should determine the speed.

I understand but I dont see how to fix it properly unless we add a
some specific STM32 properties in the DT or in the dwc2_core_params.
In fact there are two cores, and they are different in terms of
functionality (despite of the type of the PHY).
One core is for FS and other is for HS, so they could/should have
different compatible strings because they have different
configurations and are different piece of IP/Hardware(The buffer size
are different, the number of end points and so one, DMA)

Then it is perfectly fine to have 2 compatible strings: one for the FS 
block and one for the HS block.

But the problem is that the HS core can also support the the FS mode
and in this case is misleading to have a HS core with an FS compatible
string.

But as you said, there are other differences in the 2 blocks, so just 
changing to the FS compatible string would not work.

You could just have a high-speed-disable property or something, but look 
thru existing bindings and see if one exists already. If not, propose a 
common one.

Something like that (real case for STM32F429I-DISCO):

&usbotg_hs {
compatible = "st,stm32-fsotg", "snps,dwc2";
dr_mode = "host";
pinctrl-0 = <&usbotg_fs_pins_b>;
pinctrl-names = "default";
status = "okay";
};

Even if the decision is phy based it would lead to a STM32 specific
logic and we would need to figure out how to represent the internal
PHY.

Most SoCs end up describing the phys at least for USB 2 and 3 as they 
vary a lot eventhough everyone licenses one of the few IP blocks.

Rob