linux-kernel - Re: [PATCH v6 3/4] usb: dwc3: Resize TX FIFOs to meet EP bursting requirements

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Date:   Thu, 28 Jan 2021 15:08:37 -0800
From:   Wesley Cheng <wcheng@...eaurora.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org, robh+dt@...nel.org,
        agross@...nel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, peter.chen@....com,
        jackp@...eaurora.org
Subject: Re: [PATCH v6 3/4] usb: dwc3: Resize TX FIFOs to meet EP bursting
 requirements



On 1/25/2021 9:15 PM, Bjorn Andersson wrote:
> On Mon 25 Jan 22:32 CST 2021, Wesley Cheng wrote:
>> On 1/25/2021 5:55 PM, Bjorn Andersson wrote:
>>> On Mon 25 Jan 19:14 CST 2021, Wesley Cheng wrote:
>>>
>>>>
>>>>
>>>> On 1/22/2021 9:12 AM, Bjorn Andersson wrote:
>>>>> On Thu 21 Jan 22:01 CST 2021, Wesley Cheng wrote:
>>>>>
>>>>
>>>> Hi Bjorn,
>>>>>
>>>>> Under what circumstances should we specify this? And in particular are
>>>>> there scenarios (in the Qualcomm platforms) where this must not be set?
>>>>> The TXFIFO dynamic allocation is actually a feature within the DWC3
>>>> controller, and isn't specifically for QCOM based platforms.  It won't
>>>> do any harm functionally if this flag is not set, as this is meant for
>>>> enhancing performance/bandwidth.
>>>>
>>>>> In particular, the composition can be changed in runtime, so should we
>>>>> set this for all Qualcomm platforms?
>>>>>
>>>> Ideally yes, if we want to increase bandwith for situations where SS
>>>> endpoint bursting is set to a higher value.
>>>>
>>>>> And if that's the case, can we not just set it from the qcom driver?
>>>>>
>>>> Since this is a common DWC3 core feature, I think it would make more
>>>> sense to have it in DWC3 core instead of a vendor's DWC3 glue driver.
>>>>
>>>
>>> I don't have any objections to implementing it in the core driver, but
>>> my question is can we just skip the DT binding and just enable it from
>>> the vendor driver?
>>>
>>> Regards,
>>> Bjorn
>>>
>>
>> Hi Bjorn,
>>
>> I see.  I think there are some designs which don't have a DWC3 glue
>> driver, so assuming there may be other platforms using this, there may
>> not always be a vendor driver to set this.
>>
> 
> You mean that there are implementations of dwc3 without an associated
> glue driver that haven't yet realized that they need this feature?
> 
> I would suggest then that we implement the core code necessary, we
> enable it from the Qualcomm glue layer and when someone realize that
> they need this without a glue driver it's going to be trivial to add the
> DT binding.
>>
> The alternative is that we're lugging around a requirement to specify
> this property in all past, present and future Qualcomm dts files - and
> then we'll need to hard code it for ACPI anyways.
> 
Hi Bjorn,

Can we utilize the of_add_property() call to add the "tx-fifo-resize"
property from the dwc3_qcom_register_core() API?  That way at least the
above concern would be addressed.

I'm not too familiar with the ACPI design, but I do see that the
dwc3-qcom does have an array carrying some DWC3 core properties.  Looks
like we can add the tx-fifo-resize property here too.

static const struct property_entry dwc3_qcom_acpi_properties[] = {
	PROPERTY_ENTRY_STRING("dr_mode", "host"),
	{}
};


Thanks
Wesley Cheng

> Regards,
> Bjorn
> 

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