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Subject: Re: [PATCH v2] rpmsg: core: add API to get MTU
To:     Arnaud POULIQUEN <arnaud.pouliquen@st.com>,
        Ohad Ben-Cohen <ohad@wizery.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        <linux-kernel@vger.kernel.org>, <linux-remoteproc@vger.kernel.org>,
        <linux-arm-msm@vger.kernel.org>
CC:     Fabien DESSENNE <fabien.dessenne@st.com>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>
References: <20191113172249.32412-1-arnaud.pouliquen@st.com>
 <f0419672-f1a5-b909-2dff-c611f852919b@st.com>
From:   Suman Anna <s-anna@ti.com>
Message-ID: <90bec284-6a99-e75f-1609-de763048a1e2@ti.com>
Date:   Tue, 14 Jan 2020 17:40:53 -0600
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Hi Arnaud,

On 1/13/20 7:19 AM, Arnaud POULIQUEN wrote:
> Hi Bjorn, Suman,
> 
> Gentleman reminder :)

Thanks for the revised version, and very sorry about the delay.  Only
one minor nit that you missed from my comments the v6 rpmsg-tty series
[1], otherwise I am good with the changes. See below.

FWIW, I have already been using this patch on our downstream 2020 LTS
based kernel and eliminate the the need to expose the virtio_rpmsg's
rpmsg_hdr to rpmsg client drivers :).

> 
> Thank in advance,
> 
> Arnaud
> 
> On 11/13/19 6:22 PM, Arnaud Pouliquen wrote:
>> Return the rpmsg buffer MTU for sending message, so rpmsg users
>> can split a long message in several sub rpmsg buffers.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
>> ---
>>  V1 to V2
>>
>>   V1 patch:https://lore.kernel.org/patchwork/patch/1124684/
>>   - Change patch title,
>>   - as not solution today to support MTU on GLINK make ops optional,
>>     RPMsg client API returns -ENOTSUPP in this case,
>>   - suppress smd and glink patches.
>> ---
>>  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..0e56e046f5c6 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(), optional

In the description for the ops, 'mpu' is a typo. My earlier comment was
essentially,
%s/see @get_mpu()/see @rpmsg_get_mtu()/

regards
Suman

[1] https://patchwork.kernel.org/patch/11130209/

>>   *
>>   * 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..6e48fdf24555 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_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_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_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..88d7892ca93d 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 inline ssize_t rpmsg_get_mtu(struct rpmsg_endpoint *ept)
>> +{
>> +	/* 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 */
>>