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Message-ID: <f95a6dbe-f774-7778-9cd8-aba0677b9413@foss.st.com>
Date:   Thu, 15 Jun 2023 10:47:29 +0200
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Subject: Re: [PATCH V7 1/3] rpmsg: core: Add signal API support
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To:     Bjorn Andersson <andersson@kernel.org>
CC:     Sarannya S <quic_sarannya@quicinc.com>,
        <quic_bjorande@quicinc.com>, <swboyd@chromium.org>,
        <quic_clew@quicinc.com>, <mathieu.poirier@linaro.org>,
        <linux-kernel@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
        <linux-remoteproc@vger.kernel.org>,
        Deepak Kumar Singh <quic_deesin@quicinc.com>
References: <1682160127-18103-1-git-send-email-quic_sarannya@quicinc.com>
 <1682160127-18103-2-git-send-email-quic_sarannya@quicinc.com>
 <c44d8942-83e5-01ec-491b-bac1fb27de99@foss.st.com>
 <20230614152435.2quoctx6ouvw4ous@ripper>
From:   Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>
Organization: STMicroelectronics
In-Reply-To: <20230614152435.2quoctx6ouvw4ous@ripper>
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Hi,

On 6/14/23 17:24, Bjorn Andersson wrote:
> On Mon, Apr 24, 2023 at 02:49:29PM +0200, Arnaud POULIQUEN wrote:
>> Hello,
>>
>> On 4/22/23 12:42, Sarannya S wrote:
>>> From: Deepak Kumar Singh <quic_deesin@quicinc.com>
>>>
>>> Some transports like Glink support the state notifications between
>>> clients using flow control signals similar to serial protocol signals.
>>> Local glink client drivers can send and receive flow control status
>>> to glink clients running on remote processors.
>>>
>>> Add APIs to support sending and receiving of flow control status by
>>> rpmsg clients.
>>>
>>> Signed-off-by: Deepak Kumar Singh <quic_deesin@quicinc.com>
>>> Signed-off-by: Sarannya S <quic_sarannya@quicinc.com>
>>> ---
>>>  drivers/rpmsg/rpmsg_core.c     | 21 +++++++++++++++++++++
>>>  drivers/rpmsg/rpmsg_internal.h |  2 ++
>>>  include/linux/rpmsg.h          | 15 +++++++++++++++
>>>  3 files changed, 38 insertions(+)
>>>
>>> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
>>> index a2207c0..e8bbe05 100644
>>> --- a/drivers/rpmsg/rpmsg_core.c
>>> +++ b/drivers/rpmsg/rpmsg_core.c
>>> @@ -331,6 +331,25 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst,
>>>  EXPORT_SYMBOL(rpmsg_trysend_offchannel);
>>>  
>>>  /**
>>> + * rpmsg_set_flow_control() - sets/clears serial flow control signals
>>> + * @ept:	the rpmsg endpoint
>>> + * @enable:	pause/resume incoming data flow	
>>> + * @dst:	destination address of the endpoint
>>> + *
>>> + * Return: 0 on success and an appropriate error value on failure.
>>> + */
>>> +int rpmsg_set_flow_control(struct rpmsg_endpoint *ept, bool enable, u32 dst)
>>> +{
>>> +	if (WARN_ON(!ept))
>>> +		return -EINVAL;
>>> +	if (!ept->ops->set_flow_control)
>>> +		return -ENXIO;
>>
>> Here we return an error if the backend does not implement the ops.
>> But the set_flow_control ops is optional.
>> Should we return 0 instead with a debug message?
>>
> 
> It seems reasonable to allow the software to react to the absence of
> flow control support, so a debug message wouldn't help.
> 
> But advertising that more explicitly by returning something like
> EOPNOTSUPP seems better.

Right, this seems more reliable.

Thanks,
Arnaud

> 
> Regards,
> Bjorn