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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>
From:   Suman Anna <s-anna@ti.com>
Message-ID: <b338480e-c586-f988-f5b6-784551b7beb6@ti.com>
Date:   Thu, 21 May 2020 14:06:09 -0500
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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.

> 
>> Signed-off-by: Suman Anna <s-anna@ti.com>
>> ---
>>   drivers/remoteproc/remoteproc_core.c    | 25 +++++++++++++++----------
>>   drivers/remoteproc/remoteproc_debugfs.c | 17 ++++++++++-------
>>   include/linux/remoteproc.h              |  8 +++++++-
>>   3 files changed, 32 insertions(+), 18 deletions(-)
>>
> [..]
>> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
>> index 77788a4bb94e..526d3cb45e37 100644
>> --- a/include/linux/remoteproc.h
>> +++ b/include/linux/remoteproc.h
>> @@ -86,7 +86,13 @@ struct resource_table {
>>    * this header, and it should be parsed according to the resource type.
>>    */
>>   struct fw_rsc_hdr {
>> -	u32 type;
>> +	union {
>> +		u32 type;
>> +		struct {
>> +			u16 t;
>> +			u16 v;
>> +		} st;
> 
> I see your "type" is little endian...

Yeah, definitely a draw-back if we want to support big-endian rprocs. Do 
you have any remoteprocs following big-endian? All TI remoteprocs are 
little-endian except for really old ones.

regards
Suman