On 5/11/2023 2:59 AM, Thinh Nguyen wrote:
Hi,
On Wed, May 10, 2023, Krishna Kurapati PSSNV wrote:
Hi Team,
If we set maximum speed to "super-speed" for a SSP capable controller, I
see device mode working in SS but host mode still works in SSP. From the
yaml documentation of max-speed, I see the following:
maximum-speed:
description:
Tells USB controllers we want to work up to a certain speed. Incase
this isn't passed via DT, USB controllers should default to their maximum HW
capability.
Shouldn't this maximum speed get limited to gen1 even for host mode ?
The description is ambiguous here. However, we only ever use this
property to limit the speed for device mode (from what I see in the
other drivers of the kernel). Should we ever need to limit this for host
mode, IMHO, we should introduce a new property for that and clarify this
property.
Hi Thinh,
Sorry for not being clear. The following is the version and ID of
SM8550 controller: (usb31 controller)
VER_NUM: 0x3139302A
VER_TYPE: 0x67612A2A
USB3_PRI_USB31_IP_NAME (0xA60C120) = 0x33313130
We need to force this to gen-1 to fallback to SS even for host mode too
as customers are facing compliance issues on SSP.
If so, can we set LLUCTL Force_Gen1 bit if (Controller is Gen2 && max_speed
= SuperSpeed) somewhere after GCTL core soft reset is done in set_mode ?
BTW, that's for dwc_usb31. For dwc_usb32, we use a different register to
limit different eSS speeds and lanecount.
To limit to highspeed for xhci, we can disable usb3 ports (clear the
PORTSC.PP). I don't think we can force limit to full or low speed for
dwc3 host mode.
From your explanation, can I send a patch for with the following:
1. Update description for max speed
2. Add force_gen1 property and if it is set, check the version (usb31)
and set LLUCTL.Force_Gen1 bit.
Later if someone wants to add code for usb32 as well, they can reuse the
same property and extend the code for the same.
Let me know if this would be acceptable.
Regards,
Krishna,
BR,
Thinh
The reason being, there were some compliance issues seen with SSP on some of
our targets and we wanted to drop down to Gen-1 in our targets, but limiting
maximum-speed is affecting only device mode.
Regards,
Krishna,
