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

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Date:   Sat, 4 Apr 2020 19:45:48 -0600
From:   Rob Herring <robh@...nel.org>
To:     Tejas Joglekar <Tejas.Joglekar@...opsys.com>
Cc:     linux-usb@...r.kernel.org, devicetree@...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

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?

Rob