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Date:   Mon, 26 Jun 2023 17:30:07 +0200
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Subject: Re: [PATCH v3 3/6] media: dt-bindings: mediatek,vcodec: Remove
 VDEC_SYS for mt8183
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Cc:     Matthias Brugger <matthias.bgg@gmail.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
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        Andrew-CT Chen <andrew-ct.chen@mediatek.com>,
        Conor Dooley <conor+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Tiffany Lin <tiffany.lin@mediatek.com>,
        Yunfei Dong <yunfei.dong@mediatek.com>,
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From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
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On 26/06/2023 15:54, Nícolas F. R. A. Prado wrote:
> 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?

It's different compatible, so it can have different entries.


> 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?

I wrote already what I want:

  In all cases they should be defined, even by "defined" means not allowed.

Now of course the best would be if the reg-names are always the same, at
least in respect of order of items. This is what we try to do for all
devices.

> 
>>
>>>
>>> For example, for mt8173 we currently have
>>>
>>> 		vcodec_dec: vcodec@16000000 {
>>> 			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@16020000 {
>>> 			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.

So remove the reg-name now and there will be no "later"?

Best regards,
Krzysztof