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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>
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 <b338480e-c586-f988-f5b6-784551b7beb6@ti.com>
 <20200521192146.GO408178@builder.lan>
 <57ae5678-fd0a-07a8-6165-a2cf7ccdef88@ti.com>
 <20200521194116.GP408178@builder.lan>
From:   Suman Anna <s-anna@ti.com>
Message-ID: <5529e8ff-b5ed-9dd6-e7f6-55a00225c2b9@ti.com>
Date:   Thu, 21 May 2020 14:52:02 -0500
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On 5/21/20 2:41 PM, Bjorn Andersson wrote:
> On Thu 21 May 12:29 PDT 2020, Suman Anna wrote:
> 
>> 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).
>>
> 
> Right, but either you add support for new resource types to the
> loading_handlers, or you add the version checks within each handler,
> either way you will have to do some work to be compatible with new
> versions.
> 
> Regarding what resources would be fit for a 64-bit processor probably
> relates to many things, in particular the question of what we actually
> mean when we say that a coprocessor is 64-bit. So I don't really see a
> need for the remoteproc core to prevent someone to design their
> system/firmware to have a 64-bit CPU being passed 32-bit addresses.

OK. In general, I have seen firmware developers get confused w.r.t the 
resource types, that's why I was inclined to go with the restrictive 
checking. Anyway, will rework the support as per the comments.

regards
Suman