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

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Date:   Fri, 04 Jun 2021 17:18:16 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Wesley Cheng <wcheng@...eaurora.org>
Cc:     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 Wed, May 19, 2021 at 12:49:16AM -0700, Wesley Cheng wrote:
>> Changes in V9:
>>  - Fixed incorrect patch in series.  Removed changes in DTSI, as dwc3-qcom will
>>    add the property by default from the kernel.
>
> This patch series has one build failure and one warning added:
>
> drivers/usb/dwc3/gadget.c: In function ‘dwc3_gadget_calc_tx_fifo_size’:
> drivers/usb/dwc3/gadget.c:653:45: warning: passing argument 1 of ‘dwc3_mdwidth’ makes pointer from integer without a cast [-Wint-conversion]
>   653 |         mdwidth = dwc3_mdwidth(dwc->hwparams.hwparams0);
>       |                                ~~~~~~~~~~~~~^~~~~~~~~~
>       |                                             |
>       |                                             u32 {aka unsigned int}
> In file included from drivers/usb/dwc3/debug.h:14,
>                  from drivers/usb/dwc3/gadget.c:25:
> drivers/usb/dwc3/core.h:1493:45: note: expected ‘struct dwc3 *’ but argument is of type ‘u32’ {aka ‘unsigned int’}
>  1493 | static inline u32 dwc3_mdwidth(struct dwc3 *dwc)
>       |                                ~~~~~~~~~~~~~^~~
>
>
> drivers/usb/dwc3/dwc3-qcom.c: In function ‘dwc3_qcom_of_register_core’:
> drivers/usb/dwc3/dwc3-qcom.c:660:23: error: implicit declaration of function ‘of_add_property’; did you mean ‘of_get_property’? [-Werror=implicit-function-declaration]
>   660 |                 ret = of_add_property(dwc3_np, prop);
>       |                       ^~~~~~~~~~~~~~~
>       |                       of_get_property
>
>
> How did you test these?

to be honest, I don't think these should go in (apart from the build
failure) because it's likely to break instantiations of the core with
differing FIFO sizes. Some instantiations even have some endpoints with
dedicated functionality that requires the default FIFO size configured
during coreConsultant instantiation. I know of at OMAP5 and some Intel
implementations which have dedicated endpoints for processor tracing.

With OMAP5, these endpoints are configured at the top of the available
endpoints, which means that if a gadget driver gets loaded and takes
over most of the FIFO space because of this resizing, processor tracing
will have a hard time running. That being said, processor tracing isn't
supported in upstream at this moment.

I still think this may cause other places to break down. The promise the
databook makes is that increasing the FIFO size over 2x wMaxPacketSize
should bring little to no benefit, if we're not maintaining that, I
wonder if the problem is with some of the BUSCFG registers instead,
where we configure interconnect bursting and the like.

-- 
balbi

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