linux-kernel - Re: [PATCH 03/11] dt-bindings: usb: mtk-xhci: add compatible for mt8195

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Date:   Wed, 18 Aug 2021 09:20:37 -0500
From:   Rob Herring <robh@...nel.org>
To:     Chunfeng Yun (云春峰) 
        <Chunfeng.Yun@...iatek.com>
Cc:     "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>,
        Eddie Hung (洪正鑫) 
        <Eddie.Hung@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>
Subject: Re: [PATCH 03/11] dt-bindings: usb: mtk-xhci: add compatible for mt8195

On Wed, Aug 11, 2021 at 3:02 AM Chunfeng Yun (云春峰)
<Chunfeng.Yun@...iatek.com> wrote:
>
> On Fri, 2021-08-06 at 14:43 -0600, Rob Herring wrote:
> > On Fri, Jul 30, 2021 at 04:49:54PM +0800, Chunfeng Yun wrote:
> > > There are 4 USB controllers on MT8195, the controllers (IP1~IP3,
> > > exclude IP0) have a wrong default SOF/ITP interval which is
> > > calculated from the frame counter clock 24Mhz by default, but
> > > in fact, the frame counter clock is 48Mhz, so we should set
> > > the accurate interval according to 48Mhz. Here add a new compatible
> > > for MT8195, it's also supported in driver. But the first controller
> > > (IP0) has no such issue, we prefer to use generic compatible,
> > > e.g. mt8192's compatible.
> >
> > That only works until you find some 8195 bug common to all
> > instances.
> It's also OK for IP0 to use mt8195's compatible, these setting value is
> the same as IP0's default value, use mt8192's may avoid these dummy
> setting.

I still don't understand. By use mt8192's compatible, that means you
have for IP0:

compatible = "mediatek,mt8192-xhci", "mediatek,mtk-xhci";

And for the rest:
compatible = "mediatek,mt8195-xhci", "mediatek,mtk-xhci";

If there's a 8195 quirk you need to work around, then you can't on
IP0. You need to be able to address quirks in the future without
changing the DTB. That is why we require SoC specific compatibles even
when IP blocks are 'the same'.

Rob