linux-kernel - Re: [PATCH v9 0/5] Re-introduce TX FIFO resize for larger EP bursting

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Date:   Thu, 10 Jun 2021 13:16:51 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Wesley Cheng <wcheng@...eaurora.org>, agross@...nel.org,
        bjorn.andersson@...aro.org, robh+dt@...nel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        jackp@...eaurora.org, Thinh.Nguyen@...opsys.com
Subject: Re: [PATCH v9 0/5] Re-introduce TX FIFO resize for larger EP bursting


Hi,

Greg KH <gregkh@...uxfoundation.org> writes:
> On Thu, Jun 10, 2021 at 12:20:00PM +0300, Felipe Balbi wrote:
>> > As mentioned above, these changes are currently present on end user
>> > devices for the past few years, so its been through a lot of testing :).
>> 
>> all with the same gadget driver. Also, who uses USB on android devices
>> these days? Most of the data transfer goes via WiFi or Bluetooth, anyway
>> :-)
>
> I used to think that too, until I saw some of the new crazy designs
> where lots of SoC connections internally to the device run on USB.  Also
> look at the USB offload stuff as one example of how the voice sound path
> goes through the USB controller on the SoC on the latest Samsung Galaxy
> phones that are shipping now :(

yeah, that's one reason NOT to touch the FIFO sizes :-) OMAP5 has, as
mentioned before, processor trace offload via USB too. If we modify the
FIFO configuration set by the HW designer we risk loosing those features.

> There's also devices with the modem/network connection going over USB,
> along with other device types as well.  Android Auto is crazy with

yeah, and there will be more coming. USB Debug class is already
integrated in some SoCs, that gives us jtag-like access over USB.

> almost everything hooked up directly with a USB connection to the host
> system running Linux.

that's running against USB host, though, right? Android is the host, not
the gadget :-)

The FIFO sizes here are for the gadget side.

>> I guess only developers are using USB during development to flash dev
>> images heh.
>
> I wish, we are reaching the point where the stability of the overall
> Android system depends on how well the USB controller works.  We are a
> product of our success...
>
> thanks,
>
> greg k-h

-- 
balbi

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