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Subject: Re: [PATCH 2/4] remoteproc: introduce version element into resource
 type field
To:     Bjorn Andersson <bjorn.andersson@linaro.org>
CC:     Rob Herring <robh+dt@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Clement Leger <cleger@kalray.eu>,
        Loic Pallardy <loic.pallardy@st.com>,
        Arnaud Pouliquen <arnaud.pouliquen@st.com>,
        Lokesh Vutla <lokeshvutla@ti.com>,
        <linux-remoteproc@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
References: <20200325204701.16862-1-s-anna@ti.com>
 <20200325204701.16862-3-s-anna@ti.com> <20200521175421.GI408178@builder.lan>
 <b338480e-c586-f988-f5b6-784551b7beb6@ti.com>
 <20200521192146.GO408178@builder.lan>
From:   Suman Anna <s-anna@ti.com>
Message-ID: <57ae5678-fd0a-07a8-6165-a2cf7ccdef88@ti.com>
Date:   Thu, 21 May 2020 14:29:11 -0500
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On 5/21/20 2:21 PM, Bjorn Andersson wrote:
> On Thu 21 May 12:06 PDT 2020, Suman Anna wrote:
> 
>> Hi Bjorn,
>>
>> On 5/21/20 12:54 PM, Bjorn Andersson wrote:
>>> On Wed 25 Mar 13:46 PDT 2020, Suman Anna wrote:
>>>
>>>> The current remoteproc core has supported only 32-bit remote
>>>> processors and as such some of the current resource structures
>>>> may not scale well for 64-bit remote processors, and would
>>>> require new versions of resource types. Each resource is currently
>>>> identified by a 32-bit type field. Introduce the concept of version
>>>> for these resource types by overloading this 32-bit type field
>>>> into two 16-bit version and type fields with the existing resources
>>>> behaving as version 0 thereby providing backward compatibility.
>>>>
>>>> The version field is passed as an additional argument to each of
>>>> the handler functions, and all the existing handlers are updated
>>>> accordingly. Each specific handler will be updated on a need basis
>>>> when a new version of the resource type is added.
>>>>
>>>
>>> I really would prefer that we add additional types for the new
>>> structures, neither side will be compatible with new versions without
>>> enhancements to their respective implementations anyways.
>>
>> OK.
>>
>>>
>>>> An alternate way would be to introduce the new types as completely
>>>> new resource types which would require additional customization of
>>>> the resource handlers based on the 32-bit or 64-bit mode of a remote
>>>> processor, and introduction of an additional mode flag to the rproc
>>>> structure.
>>>>
>>>
>>> What would this "mode" indicate? If it's version 0 or 1?
>>
>> No, for indicating if the remoteproc is 32-bit or 64-bit and adjust the
>> loading handlers if the resource types need to be segregated accordingly.
>>
> 
> Sorry, I think I'm misunderstanding something. Wouldn't your 64-bit
> remote processor need different firmware from your 32-bit processor
> anyways, if you want to support the wider resource? And you would pack
> your firmware with the appropriate resource types?

Yes, that's correct.

> 
> Afaict the bit width of your remote processor, busses or memory is
> unrelated to the choice of number of bits used to express things in the
> resource table.

I would have to add the new resource type to the loading_handlers right, 
so it is a question of whether we want to impose any restrictions in 
remoteproc core or not from supporting a certain resource type (eg: I 
don't expect RSC_TRACE entries on 64-bit processors).

regards
Suman