Re: [PATCH] dt-bindings: usb: dwc3: Add snps,enable_guctl1_ipd_quirk
From: Conor Dooley
Date: Thu Feb 15 2024 - 14:39:46 EST
On Fri, Feb 16, 2024 at 12:31:05AM +0530, Radhey Shyam Pandey wrote:
> From: Piyush Mehta <piyush.mehta@xxxxxxx>
>
> SNPS controller when configured in HOST mode maintains Inter Packet
> Delay (IPD) of ~380ns which works with most of the super-speed hubs
> except VIA-LAB hubs. When IPD is ~380ns HOST controller fails to
> enumerate FS/LS devices when connected behind VIA-LAB hubs.
>
> To address the above issue, add 'snps,enable_guctl1_ipd_quirk' quirk,
> This quirk set the bit 9 of GUCTL1 that enables the workaround in HW to
> reduce the ULPI clock latency by 1 cycle, thus reducing the IPD (~360ns).
>
> Signed-off-by: Piyush Mehta <piyush.mehta@xxxxxxx>
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxx>
> ---
> In the zynqmp public database GUCTL1 bit 9 is reserved but it is used to
> enable a fix related to Inter Packet Delay in HW. The documentation team
> is working to update GUCTL1 bit 9 description.
Does this just affect the zynqmp?
If it does, then you don't need a property - do this based on
compatible.
If it does affect other devices, what prevents the workaround being
performed for all dwc3 controllers?
Cheers,
Conor.
> ---
> Documentation/devicetree/bindings/usb/snps,dwc3.yaml | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> index 8f5d250070c7..b226457a6e50 100644
> --- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> +++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> @@ -280,6 +280,13 @@ properties:
> xhci reset. And the vbus will back to 5V automatically when reset done.
> type: boolean
>
> + snps,enable_guctl1_ipd_quirk:
No underscores in properties please.
> + description:
> + When set, HW reduce the ULPI clock latency by 1 cycle, thus reducing
> + the IPD (~360ns) and making controller enumerate FS/LS devices
> + connected behind via-hubs.
> + type: boolean
> +
> snps,is-utmi-l1-suspend:
> description:
> True when DWC3 asserts output signal utmi_l1_suspend_n, false when
> --
> 2.34.1
>
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