linux-kernel - Re: [PATCH v29 04/33] xhci: sideband: add initial api to register a sideband entity

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Message-ID: <52ea0b32-79c7-42e8-8e2c-192d08f41e64@quicinc.com>
Date: Tue, 29 Oct 2024 11:58:03 -0700
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC: "srinivas.kandagatla@...aro.org" <srinivas.kandagatla@...aro.org>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>,
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        Mathias Nyman <mathias.nyman@...ux.intel.com>
Subject: Re: [PATCH v29 04/33] xhci: sideband: add initial api to register a
 sideband entity

Hi Thinh,

On 10/25/2024 4:22 PM, Thinh Nguyen wrote:
> Hi,
>
> On Tue, Oct 15, 2024, Wesley Cheng wrote:
>> From: Mathias Nyman <mathias.nyman@...ux.intel.com>
>>
>> Introduce XHCI sideband, which manages the USB endpoints being requested by
>> a client driver.  This is used for when client drivers are attempting to
>> offload USB endpoints to another entity for handling USB transfers.  XHCI
>> sideband will allow for drivers to fetch the required information about the
>> transfer ring, so the user can submit transfers independently.  Expose the
>> required APIs for drivers to register and request for a USB endpoint and to
>> manage XHCI secondary interrupters.
>>
>> Multiple ring segment page linking, proper endpoint clean up, and allowing
>> module compilation added by Wesley Cheng to complete original concept code
>> by Mathias Nyman.
>>
>> Signed-off-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
>> Co-developed-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> ---
>>  drivers/usb/host/Kconfig          |   9 +
>>  drivers/usb/host/Makefile         |   2 +
>>  drivers/usb/host/xhci-sideband.c  | 424 ++++++++++++++++++++++++++++++
>>  drivers/usb/host/xhci.h           |   4 +
>>  include/linux/usb/xhci-sideband.h |  70 +++++
>>  5 files changed, 509 insertions(+)
>>  create mode 100644 drivers/usb/host/xhci-sideband.c
>>  create mode 100644 include/linux/usb/xhci-sideband.h
>>
>> diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
>> index 4448d0ab06f0..96659efa4be5 100644
>> --- a/drivers/usb/host/Kconfig
>> +++ b/drivers/usb/host/Kconfig
>> @@ -104,6 +104,15 @@ config USB_XHCI_RZV2M
>>  	  Say 'Y' to enable the support for the xHCI host controller
>>  	  found in Renesas RZ/V2M SoC.
>>  
>> +config USB_XHCI_SIDEBAND
>> +	tristate "xHCI support for sideband"
>> +	help
>> +	  Say 'Y' to enable the support for the xHCI sideband capability.
>> +	  Provide a mechanism for a sideband datapath for payload associated
> Please correct me if I'm wrong, but this doesn't look like the actual
> xHCI Audio Sideband capability described in the xHCI spec section 7.9
> but rather a specific implementation for Qcom right? For the xHCI Audio
> Sideband xHCI capability, the driver should detect this capability
> through the xHCI get extended capability. If this is not xHCI Audio
> Sideband capability, we should properly clarify this in the
> documentation and the naming of things to avoid any confusion.

Sure, that's a good point.  It does still currently rely on utilizing the system memory for USB IO transfers.  I can add some comments and update some of the documentation to reflect that this is different. 

Thanks

Wesley Cheng

> I believe your implementation still needs to provide the data to the
> host controller through the system memory right? The xHCI Audio Sideband
> capability may pass the data to the xHC other than the main memory.
>
> BR,
> Thinh
>
>> +	  with audio class endpoints. This allows for an audio DSP to use
>> +	  xHCI USB endpoints directly, allowing CPU to sleep while playing
>> +	  audio.
>> +
>>  config USB_XHCI_TEGRA
>>  	tristate "xHCI support for NVIDIA Tegra SoCs"
>>  	depends on PHY_TEGRA_XUSB