linux-kernel - Re: [PATCH v3 3/6] media: dt-bindings: mediatek,vcodec: Remove VDEC

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Message-ID: <aef120c8-bb25-476f-8976-7f699a851334@notapiano>
Date:   Mon, 26 Jun 2023 09:54:20 -0400
From:   Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, kernel@...labora.com,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Yunfei Dong <yunfei.dong@...iatek.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v3 3/6] media: dt-bindings: mediatek,vcodec: Remove
 VDEC_SYS for mt8183

On Fri, Jun 23, 2023 at 06:21:31PM +0200, Krzysztof Kozlowski wrote:
> On 21/06/2023 20:00, Nícolas F. R. A. Prado wrote:
> >>
> >> But anyway this variant comes with some set of regs and reg-names. Other
> >> variant comes with different set. In all cases they should be defined,
> >> even by "defined" means not allowed.
> > 
> > I'm not sure what you mean. Are you suggesting to disable reg-names on mt8173?
> 
> That's one of the options if for some reason you don't want to define them.
> 
> > 
> >>
> >>>
> >>> But in a separate series we could drop vdecsys from mt8173's reg as well,
> >>> passing it as a syscon instead, which would solve the warning on that platform,
> >>> though some more driver changes would be needed to be able to handle it for that
> >>> SoC. The newer SoCs like mt8192, mt8195, etc, should also get vdecsys dropped
> >>> from their regs to have a correct memory description.
> >>>
> >>
> >> Sure, but I don't understand how does it affect defining and making
> >> specific regs/reg-names or keeping them loose.
> > 
> > We need some way to tell in the driver whether the first reg is VDEC_SYS or not.
> > Since so far reg-names have not been used for the vcodec, the simplest, and
> > cleanest, way to do it, is to add reg-names when VDEC_SYS is not present. When
> > the other SoCs are updated to no longer have the first reg as VDEC_SYS, they
> > would also have reg-names added to their binding, to clearly indicate that.
> 
> Don't use reg-names for that. The order of entries is anyway strict.

Since the order of entries is strict, if I remove VDEC_SYS from mt8183, I also
need to remove it from mt8173, is that what you mean? I would still check for
the presence of reg-names in the driver to differentiate whether the old or new
binding is used, you just don't want different reg-names between compatibles in
the binding?

> 
> > 
> > For example, for mt8173 we currently have
> > 
> > 		vcodec_dec: vcodec@...00000 {
> > 			compatible = "mediatek,mt8173-vcodec-dec";
> > 			reg = <0 0x16000000 0 0x100>,	/* VDEC_SYS */
> > 			      <0 0x16020000 0 0x1000>,	/* VDEC_MISC */
> > 			      <0 0x16021000 0 0x800>,	/* VDEC_LD */
> > 			      <0 0x16021800 0 0x800>,	/* VDEC_TOP */
> > 			      <0 0x16022000 0 0x1000>,	/* VDEC_CM */
> > 			      <0 0x16023000 0 0x1000>,	/* VDEC_AD */
> > 			      <0 0x16024000 0 0x1000>,	/* VDEC_AV */
> > 			      <0 0x16025000 0 0x1000>,	/* VDEC_PP */
> > 			      <0 0x16026800 0 0x800>,	/* VDEC_HWD */
> > 			      <0 0x16027000 0 0x800>,	/* VDEC_HWQ */
> > 			      <0 0x16027800 0 0x800>,	/* VDEC_HWB */
> > 			      <0 0x16028400 0 0x400>;	/* VDEC_HWG */
> > 
> > In a future series, when removing VDEC_SYS from it, it would become
> > 
> > 		vcodec_dec: vcodec@...20000 {
> > 			compatible = "mediatek,mt8173-vcodec-dec";
> > 			reg = <0 0x16020000 0 0x1000>,	/* VDEC_MISC */
> > 			      <0 0x16021000 0 0x800>,	/* VDEC_LD */
> > 			      <0 0x16021800 0 0x800>,	/* VDEC_TOP */
> > 			      <0 0x16022000 0 0x1000>,	/* VDEC_CM */
> > 			      <0 0x16023000 0 0x1000>,	/* VDEC_AD */
> > 			      <0 0x16024000 0 0x1000>,	/* VDEC_AV */
> > 			      <0 0x16025000 0 0x1000>,	/* VDEC_PP */
> > 			      <0 0x16026800 0 0x800>,	/* VDEC_HWD */
> > 			      <0 0x16027000 0 0x800>,	/* VDEC_HWQ */
> > 			      <0 0x16027800 0 0x800>,	/* VDEC_HWB */
> > 			      <0 0x16028400 0 0x400>;	/* VDEC_HWG */
> > 			reg-names = "misc", "ld", "top", "cm", "ad", "av", "pp",
> >                                     "hwd", "hwq", "hwb", "hwg";
> 
> So you want to use reg-names to avoid ABI break. This is not the reason
> not to define reg-names for other case.

There will be an ABI break anyway when the first reg is removed (as shown
above), I'm just trying to avoid churn: adding a reg-name that will be removed
later.

Thanks,
Nícolas