Hello,

My take to the purpose of calling XhcEvaluateContext/XhcEvaluateContext64 functions is to “inform the xHC of the change to the Default Control endpoint’s Max Packet Size parameter.”

That is why the function only set bit 1 (Add Context bit 1) to inform the xHC only Endpoint Context for EP0 should be evaluated by xHC:

  InputContext->InputControlContext.Dword2 |= BIT1

I checked the xHCI spec, it does not prohibit only setting Add Context bit 1. According to section 4.6.7 Evaluate Context:

System software shall initialize Contexts of the

Input Context affected by the command. All Contexts not referenced by an Add Context flag in the Input

Context are ignored by the xHC.

If this is the case, the Slot Context should be ignored by the xHC, since Add Context bit 0 is cleared.

Then, according to section 6.2.3.3 Evaluate Context Command Usage:

A 'valid' Input Endpoint Context for an Evaluate Context Command requires that if the Add Context flag

(A1) for Default Control Endpoint is set to ‘1’, the Max Packet Size field shall be evaluated.

I do not think below code snippet violates with the above content in the spec:

  ZeroMem (InputContext, sizeof (INPUT_CONTEXT_64));

  InputContext->InputControlContext.Dword2 |= BIT1;

  InputContext->EP[0].MaxPacketSize         = MaxPacketSize;

Do you have a chance to test other USB devices on your environment? Is it possible that the issue is a device specific case?

Thanks in advance.

Best Regards,

Hao Wu

From: Jiading Zhang <jdzhang@kunluntech.com.cn>
Sent: Wednesday, September 14, 2022 5:23 PM
To: Wu; Wu, Hao A <hao.a.wu@intel.com>; devel@edk2.groups.io
Subject: Re: [edk2-devel] [PATCH] MdeModulePkg/Bus/Pci/XhciDxe: Fix the Bug of clean InputContext in XhcEvaluateContext64();

When I use the newest XhciDxe driver in Phytium Platform( ARM) ,  I found if clearing “Input Context” in XhcEvaluateContext64(), the usb KB doesn't work, and mark the  code   ZeroMem (InputContext, sizeof (INPUT_CONTEXT_64));  it works. 
I viewed the code again, maybe change the ZeroMem (InputContext, sizeof (INPUT_CONTEXT_64)); to ZeroMem (InputContext, sizeof (INPUT_CONTRL_CONTEXT_64)); is more resonable.  Because when clearing the INPUT_CONTEXT_64, the Slot context and the endpoint context are cleared too. But according the xHCI Spec section 6.2.2 
Note：Unless otherwise stated: As Input, all fields of the Slot Context shall be initialized to the appropriate value by software before issuing a command.
And I test again, just clear INPUT_CONTRL_CONTEXT_64 is OK.