linux-kernel - Re: [PATCH v7 1/2] rpmsg: core: add API to get MTU

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Date:   Wed, 1 Apr 2020 08:29:35 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Arnaud Pouliquen <arnaud.pouliquen@...com>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suman Anna <s-anna@...com>,
        Fabien DESSENNE <fabien.dessenne@...com>,
        linux-stm32@...md-mailman.stormreply.com,
        xiang xiao <xiaoxiang781216@...il.com>
Subject: Re: [PATCH v7 1/2] rpmsg: core: add API to get MTU

On 01. 04. 20, 8:28, Jiri Slaby wrote:
> On 24. 03. 20, 18:04, 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@...com>
>> Acked-by: Suman Anna <s-anna@...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;
> 
> Hmm, I don't think all callers of tty_write_room() handle negative values...
> 
> But some drivers also return negative values. There is some work to be
> done, adding to TODO.
> 
> For the time being, I suggest returning 0 instead.

Or better, convert the negative to 0 in rpmsg_tty_write_room for now.

> thanks,-- 
-- 
js
suse labs