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Subject: Re: [PATCH v6 1/2] rpmsg: core: add API to get message length
To:     Suman Anna <s-anna@ti.com>, Ohad Ben-Cohen <ohad@wizery.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        xiang xiao <xiaoxiang781216@gmail.com>,
        <linux-kernel@vger.kernel.org>, <linux-remoteproc@vger.kernel.org>
CC:     Fabien DESSENNE <fabien.dessenne@st.com>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>
References: <1567602594-2913-1-git-send-email-arnaud.pouliquen@st.com>
 <1567602594-2913-2-git-send-email-arnaud.pouliquen@st.com>
 <704fadc2-3a62-5d23-6959-2495b497b3f9@ti.com>
From:   Arnaud Pouliquen <arnaud.pouliquen@st.com>
Message-ID: <399f278a-13a9-7dc8-a232-8b0ac737abdb@st.com>
Date:   Wed, 4 Sep 2019 19:30:51 +0200
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Hi Suman

On 9/4/19 6:36 PM, Suman Anna wrote:
> Hi Arnaud,
> 
> On 9/4/19 8:09 AM, Arnaud Pouliquen wrote:
>> Return the rpmsg buffer size for sending message, so rpmsg users
>> can split a long message in several sub rpmsg buffers.
> 
> Couple more minor comments..
> 
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
>> ---
>>   drivers/rpmsg/rpmsg_core.c       | 21 +++++++++++++++++++++
>>   drivers/rpmsg/rpmsg_internal.h   |  2 ++
>>   drivers/rpmsg/virtio_rpmsg_bus.c | 10 ++++++++++
>>   include/linux/rpmsg.h            | 10 ++++++++++
>>   4 files changed, 43 insertions(+)
>>
>> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
>> index e330ec4dfc33..a6ef54c4779a 100644
>> --- a/drivers/rpmsg/rpmsg_core.c
>> +++ b/drivers/rpmsg/rpmsg_core.c
>> @@ -283,6 +283,27 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst,
>>   }
>>   EXPORT_SYMBOL(rpmsg_trysend_offchannel);
>>   
>> +/**
>> + * rpmsg_get_mtu() - get maximum transmission buffer size for sending message.
>> + * @ept: the rpmsg endpoint
>> + *
>> + * This function returns maximum buffer size available for a single message.
>> + *
>> + * Return: the maximum transmission size on success and an appropriate error
>> + * value on failure.
>> + */
>> +
>> +ssize_t rpmsg_get_mtu(struct rpmsg_endpoint *ept)
>> +{
>> +	if (WARN_ON(!ept))
>> +		return -EINVAL;
>> +	if (!ept->ops->get_mtu)
>> +		return -ENOTSUPP;
>> +
>> +	return ept->ops->get_mtu(ept);
>> +}
>> +EXPORT_SYMBOL(rpmsg_get_mtu);
>> +
>>   /*
>>    * match an rpmsg channel with a channel info struct.
>>    * this is used to make sure we're not creating rpmsg devices for channels
>> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
>> index 3fc83cd50e98..12b9e72adc75 100644
>> --- a/drivers/rpmsg/rpmsg_internal.h
>> +++ b/drivers/rpmsg/rpmsg_internal.h
>> @@ -47,6 +47,7 @@ struct rpmsg_device_ops {
>>    * @trysendto:		see @rpmsg_trysendto(), optional
>>    * @trysend_offchannel:	see @rpmsg_trysend_offchannel(), optional
>>    * @poll:		see @rpmsg_poll(), optional
>> + * @get_mtu:		see @get_mpu(), required
> 
> see @rpmsg_get_mtu(). Isn't this optional atm, since we haven't added
> the callback for SMD transport?

It is a good point.
On one side, if optional, rpmsg_get_mtu returns an error and the rpmsg 
client has to define a default value, but which one?
On the other, if required, i need to implement it for SMD and Glink 
driver. Calculate the mtu for these implementations does not seems 
trivial (if possible...). And i don't know how to test dev on these 
platforms.

Any suggestions?

Regards
Arnaud

> 
>>    *
>>    * Indirection table for the operations that a rpmsg backend should implement.
>>    * In addition to @destroy_ept, the backend must at least implement @send and
>> @@ -66,6 +67,7 @@ struct rpmsg_endpoint_ops {
>>   			     void *data, int len);
>>   	__poll_t (*poll)(struct rpmsg_endpoint *ept, struct file *filp,
>>   			     poll_table *wait);
>> +	ssize_t (*get_mtu)(struct rpmsg_endpoint *ept);
>>   };
>>   
>>   int rpmsg_register_device(struct rpmsg_device *rpdev);
>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
>> index 376ebbf880d6..fab01b67a550 100644
>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
>> @@ -175,6 +175,7 @@ static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data,
>>   				  int len, u32 dst);
>>   static int virtio_rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src,
>>   					   u32 dst, void *data, int len);
>> +static ssize_t virtio_rpmsg_get_buf_mtu(struct rpmsg_endpoint *ept);
>>   
>>   static const struct rpmsg_endpoint_ops virtio_endpoint_ops = {
>>   	.destroy_ept = virtio_rpmsg_destroy_ept,
>> @@ -184,6 +185,7 @@ static const struct rpmsg_endpoint_ops virtio_endpoint_ops = {
>>   	.trysend = virtio_rpmsg_trysend,
>>   	.trysendto = virtio_rpmsg_trysendto,
>>   	.trysend_offchannel = virtio_rpmsg_trysend_offchannel,
>> +	.get_mtu = virtio_rpmsg_get_buf_mtu,
>>   };
>>   
>>   /**
>> @@ -699,6 +701,14 @@ static int virtio_rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src,
>>   	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false);
>>   }
>>   
>> +static ssize_t virtio_rpmsg_get_buf_mtu(struct rpmsg_endpoint *ept)
>> +{
>> +	struct rpmsg_device *rpdev = ept->rpdev;
>> +	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
>> +
>> +	return vch->vrp->buf_size - sizeof(struct rpmsg_hdr);
>> +}
>> +
>>   static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
>>   			     struct rpmsg_hdr *msg, unsigned int len)
>>   {
>> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
>> index 9fe156d1c018..9d638bf2bdce 100644
>> --- a/include/linux/rpmsg.h
>> +++ b/include/linux/rpmsg.h
>> @@ -135,6 +135,8 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst,
>>   __poll_t rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp,
>>   			poll_table *wait);
>>   
>> +ssize_t rpmsg_get_mtu(struct rpmsg_endpoint *ept);
>> +
>>   #else
>>   
>>   static inline int register_rpmsg_device(struct rpmsg_device *dev)
>> @@ -242,6 +244,14 @@ static inline __poll_t rpmsg_poll(struct rpmsg_endpoint *ept,
>>   	return 0;
>>   }
>>   
>> +static ssize_t rpmsg_get_mtu(struct rpmsg_endpoint *ept)
> 
> static inline
> 
> regards
> Suman
> 
>> +{
>> +	/* This shouldn't be possible */
>> +	WARN_ON(1);
>> +
>> +	return -ENXIO;
>> +}
>> +
>>   #endif /* IS_ENABLED(CONFIG_RPMSG) */
>>   
>>   /* use a macro to avoid include chaining to get THIS_MODULE */
>>
>