linux-kernel - Re: [PATCH 2/2] soc: qcom: smp2p: Add support for smp2p v2

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Message-ID: <15617371-0b20-4326-8e08-2c20b3d3c767@oss.qualcomm.com>
Date: Tue, 21 Oct 2025 11:39:38 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Deepak Kumar Singh <quic_deesin@...cinc.com>,
        Jingyi Wang <jingyi.wang@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chris Lew <chris.lew@....qualcomm.com>
Subject: Re: [PATCH 2/2] soc: qcom: smp2p: Add support for smp2p v2

On 10/21/25 10:23 AM, Deepak Kumar Singh wrote:
> 
> 
> On 9/24/2025 8:27 PM, Konrad Dybcio wrote:
>> On 9/24/25 6:18 AM, Jingyi Wang wrote:
>>> From: Chris Lew <chris.lew@....qualcomm.com>
>>>
>>> Some remoteproc need smp2p v2 support, mirror the version written by the
>>> remote if the remote supports v2. This is needed if the remote does not
>>> have backwards compatibility with v1. And reset entry last value on SSR for
>>> smp2p v2.
>>>
>>> Signed-off-by: Chris Lew <chris.lew@....qualcomm.com>
>>> Co-developed-by: Jingyi Wang <jingyi.wang@....qualcomm.com>
>>> Signed-off-by: Jingyi Wang <jingyi.wang@....qualcomm.com>
>>> ---
>>
>> [...]
>>
>>> +static int qcom_smp2p_in_version(struct qcom_smp2p *smp2p)
>>> +{
>>> +    unsigned int smem_id = smp2p->smem_items[SMP2P_INBOUND];
>>> +    unsigned int pid = smp2p->remote_pid;
>>> +    struct smp2p_smem_item *in;
>>> +    size_t size;
>>> +
>>> +    in = qcom_smem_get(pid, smem_id, &size);
>>> +    if (IS_ERR(in))
>>> +        return 0;
>>> +
>>> +    return in->version;
>>
>> are in and out versions supposed to be out of sync in case of
>> error?
>>
> I think that should be ok. If we return error smp2p connection will be completely broken. With default version 1 partial features can be supported even if remote is using version 2. Some features like smp2p connection after subsystem restart may be affected by this.>> +}

Perhaps a different question is in order.. do we ever expect smem_get to
fail under normal conditions?

[...]

>>>       /*
>>>        * Make sure the rest of the header is written before we validate the
>>>        * item by writing a valid version number.
>>>        */
>>>       wmb();
>>> -    out->version = 1;
>>> +    out->version = (in_version) ? in_version : 1;
>>
>> = in_version ?: 1
>>
>> Konrad
>>
> We want to assign in_version when value is 1/2 and 1 if value is 0 i.e. error case.

That's what this syntax does, with less characters

Konrad