Re: [RESENDING RFC PATCH 1/4] dt-bindings: usb: Add snps,consolidate-sgl & consolidate-sgl

[Felipe Balbi]

Hi,

Tejas Joglekar <Tejas.Joglekar@xxxxxxxxxxxx> writes:
> Hi,
> On 4/5/2020 7:15 AM, Rob Herring wrote:
>> On Fri, Mar 27, 2020 at 03:11:56PM +0530, Tejas Joglekar wrote:
>>> This commit adds the documentation for consolidate-sgl, and
>>> snps,consolidate-sgl property. These when set enables the quirk for
>>> XHCI driver for consolidation of sg list into a temporary buffer when small
>>> buffer sizes are scattered over the sg list not making up to MPS or total
>>> transfer size within TRB cache size with Synopsys xHC.
>>>
>>> Signed-off-by: Tejas Joglekar <joglekar@xxxxxxxxxxxx>
>>> ---
>>>  Documentation/devicetree/bindings/usb/dwc3.txt     | 3 +++
>>>  Documentation/devicetree/bindings/usb/usb-xhci.txt | 3 +++
>>>  2 files changed, 6 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/usb/dwc3.txt b/Documentation/devicetree/bindings/usb/dwc3.txt
>>> index 9946ff9ba735..292d1f7969e4 100644
>>> --- a/Documentation/devicetree/bindings/usb/dwc3.txt
>>> +++ b/Documentation/devicetree/bindings/usb/dwc3.txt
>>> @@ -104,6 +104,9 @@ Optional properties:
>>>  			this and tx-thr-num-pkt-prd to a valid, non-zero value
>>>  			1-16 (DWC_usb31 programming guide section 1.2.3) to
>>>  			enable periodic ESS TX threshold.
>>> + - snps,consolidate-sgl: enable sg list consolidation - host mode only. Set to use
>>> +			SG buffers of at least MPS size by consolidating smaller SG
>>> +			buffers list into a single buffer.
>> 
>> The preference is not to keep adding properties for every single quirk 
>> or feature. These should be implied by specific compatibles. As Synopsys 
>> knows what quirks/errata/features are in each version of IP, the 
>> compatible strings should reflect those versions. (And yes, I'm sure 
>> there's customer ECO fixes that aren't reflected in the version, but 
>> that's why we have SoC specific compatibles too.) This is the only way 
>> we can fix quirks in the OS without doing DT updates. For comparison, do 
>> you want to have to update your PC BIOS so an OS can work-around issues?
>>
> Yes, I understand what you want to say here. But I think this compatible string
> does not work with the platform drivers with PCI based systems. So based on the vendor 
> id and device id then I need to set the quirk required. 
>
> @Felipe: What do you suggest for setting up quirk without the DT update for dwc3?

We have been using Synopsys controller's revision register, but that's
not visible to xhci driver and we don't have a separate compatible for
each synopsys version on the xhci driver side. One option would be to
add "snps,xhci-foo-bar" to xhci-plat and use that.

-- 
balbi

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