Re: [RFC PATCH 2/2] rpmsg: virtio_rpmsg_bus: get buffer size from config space

[Tanmay Shah <tanmay.shah@amd.com>]

On 12/3/25 1:35 PM, Michael S. Tsirkin wrote:
> On Wed, Dec 03, 2025 at 12:12:46PM -0600, Tanmay Shah wrote:
>> Hello,
>>
>> Thanks for your reviews. Please find the response below.
>>
>> On 11/22/25 6:05 AM, Zhongqiu Han wrote:
>>> On 11/15/2025 2:46 AM, Tanmay Shah wrote:
>>>> From: Xiang Xiao <xiaoxiang781216@gmail.com>
>>>>

[...]

>>
>> Thanks, that's a good question. I keept id 2 unmodified from the original
>> series. I don't know why ID 2 was chosen in the original series. I will have
>> to discuss this with the linux remoteproc/rpmsg maintainers and choose the
>> correct ID.
>>
>> I don't see any problem choosing ID 1, but for some reason if ID 1 was
>> assigned and deprecated (I don't think that is the case) then only we should
>> use ID 2.
>>
>>
>> Arnaud, Mathieu, Bjorn any input here?
>>
>>>> +
>>>> +struct virtio_rpmsg_config {
>>>> +    /* The tx/rx individual buffer size(if VIRTIO_RPMSG_F_BUFSZ) */
>>>> +    __u32 txbuf_size;
>>>> +    __u32 rxbuf_size;
>>>> +    __u32 reserved[14]; /* Reserve for the future use */
>>>
>>> Should we use __virtio32 instead of __u32 to avoid endianness issues?
>>>
>>>
>>
>> Sure, if that is the standard in other virtio headers I will modify it.
>>
>> Thanks,
>> Tanmay
> 
> rpmsg is still not standardized, sadly. It's really time it was.
> 
> 
> 
> Modern virtio devices use __le32.
> Accordingly, accessed with virtio_cread_le
> 
> 
> __virtioXX and virtio_cread are for legacy compatible parts of config space.
> 

As of now, I am using virtio_cread so I think it is legacy compatible.

> 
> Does rpmsg want to be modern or keep using legacy? I donnu.
>

I don't know either. This we have to discuss with the maintainers and 
other vendors.


> Ideally it should finally be documented and at that point we
> definitely will want to switch to __le32.
> 
> 
> For now, run sparse to make sure you don't introduce new endian-ness
> issues.

Ack.

> 
> 



>>>> +    /* Put the customize config here */
>>>> +} __attribute__((packed));
>>>> +
>>>> +#endif /* _LINUX_VIRTIO_RPMSG_H */
>>>
>>>
>