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

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Date:   Thu, 16 Apr 2020 16:37:30 +0000
From:   Tejas Joglekar <Tejas.Joglekar@...opsys.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Tejas Joglekar <Tejas.Joglekar@...opsys.com>,
        Rob Herring <robh@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        John Youn <John.Youn@...opsys.com>
Subject: Re: [RESENDING RFC PATCH 1/4] dt-bindings: usb: Add
 snps,consolidate-sgl & consolidate-sgl

Hi,
On 4/16/2020 1:52 PM, Felipe Balbi wrote:
> 
> Hi,
> 
> Tejas Joglekar <Tejas.Joglekar@...opsys.com> 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@...opsys.com>
>>>> ---
>>>>  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.
> 
@Felipe: Thanks for suggestion

@Mathias: Do you prefer parameter passed this way? I can send the v2 patch set,
after your input.


Thanks & Regards,
 Tejas Joglekar