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From:   Felipe Balbi <balbi@kernel.org>
To:     Tejas Joglekar <Tejas.Joglekar@synopsys.com>,
        Rob Herring <robh@kernel.org>,
        Tejas Joglekar <Tejas.Joglekar@synopsys.com>
Cc:     "linux-usb\@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "devicetree\@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        John Youn <John.Youn@synopsys.com>
Subject: Re: [RESENDING RFC PATCH 1/4] dt-bindings: usb: Add snps,consolidate-sgl & consolidate-sgl
In-Reply-To: <fe59318a-b3dd-c6af-702e-1ca4aed04a8b@synopsys.com>
References: <cover.1585297723.git.joglekar@synopsys.com> <8a9ca8e08d7c4957789a209c77589f1aa4bd2f06.1585297723.git.joglekar@synopsys.com> <20200405014548.GA25539@bogus> <fe59318a-b3dd-c6af-702e-1ca4aed04a8b@synopsys.com>
Date:   Thu, 16 Apr 2020 11:22:29 +0300
Message-ID: <874ktjsuuy.fsf@kernel.org>
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Hi,

Tejas Joglekar <Tejas.Joglekar@synopsys.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 s=
mall
>>> buffer sizes are scattered over the sg list not making up to MPS or tot=
al
>>> transfer size within TRB cache size with Synopsys xHC.
>>>
>>> Signed-off-by: Tejas Joglekar <joglekar@synopsys.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/Documenta=
tion/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.
>>=20
>> The preference is not to keep adding properties for every single quirk=20
>> or feature. These should be implied by specific compatibles. As Synopsys=
=20
>> knows what quirks/errata/features are in each version of IP, the=20
>> compatible strings should reflect those versions. (And yes, I'm sure=20
>> there's customer ECO fixes that aren't reflected in the version, but=20
>> that's why we have SoC specific compatibles too.) This is the only way=20
>> we can fix quirks in the OS without doing DT updates. For comparison, do=
=20
>> 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=20
> id and device id then I need to set the quirk required.=20
>
> @Felipe: What do you suggest for setting up quirk without the DT update f=
or 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.

=2D-=20
balbi

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