linux-kernel - Re: [PATCH 2/2] tty: add rpmsg driver

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Date:   Fri, 5 Apr 2019 12:50:27 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Johan Hovold <johan@...nel.org>
CC:     Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-remoteproc@...r.kernel.org" <linux-remoteproc@...r.kernel.org>,
        Benjamin GAIGNARD <benjamin.gaignard@...com>,
        Arnaud POULIQUEN <arnaud.pouliquen@...com>
Subject: Re: [PATCH 2/2] tty: add rpmsg driver

Hi Johan,


On 03/04/2019 10:44 AM, Johan Hovold wrote:
> On Thu, Mar 21, 2019 at 04:47:19PM +0100, Fabien Dessenne wrote:
>> This driver exposes a standard tty interface on top of the rpmsg
>> framework through the "rpmsg-tty-channel" rpmsg service.
>>
>> This driver supports multi-instances, offering a /dev/ttyRPMSGx entry
>> per rpmsg endpoint.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...com>
>> Signed-off-by: Fabien Dessenne <fabien.dessenne@...com>
>> ---
>>   drivers/tty/Kconfig     |   9 ++
>>   drivers/tty/Makefile    |   1 +
>>   drivers/tty/rpmsg_tty.c | 309 ++++++++++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 319 insertions(+)
>>   create mode 100644 drivers/tty/rpmsg_tty.c
>> +static int rpmsg_tty_write(struct tty_struct *tty, const unsigned char *buf,
>> +			   int total)
>> +{
>> +	int count, ret = 0;
>> +	const unsigned char *tbuf;
>> +	struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
>> +	struct rpmsg_device *rpdev;
>> +	int msg_size;
>> +
>> +	if (!cport) {
>> +		dev_err(tty->dev, "cannot get cport\n");
>> +		return -ENODEV;
>> +	}
>> +
>> +	rpdev = cport->rpdev;
>> +
>> +	dev_dbg(&rpdev->dev, "%s: send message from tty->index = %d\n",
>> +		__func__, tty->index);
>> +
>> +	if (!buf) {
>> +		dev_err(&rpdev->dev, "buf shouldn't be null.\n");
>> +		return -ENOMEM;
>> +	}
>> +
>> +	msg_size = rpmsg_get_buf_payload_size(rpdev->ept);
>> +	if (msg_size < 0)
>> +		return msg_size;
>> +
>> +	count = total;
>> +	tbuf = buf;
>> +	do {
>> +		/* send a message to our remote processor */
>> +		ret = rpmsg_send(rpdev->ept, (void *)tbuf,
>> +				 min(count, msg_size));
> Just a drive-by comment; it looks like rpmsg_send() may block, but
> the tty-driver write() callback must never sleep.


OK, I will use rpmsg_trysend() which does not block.


BR,

Fabien


>
>> +		if (ret) {
>> +			dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
>> +			return ret;
>> +		}
>> +
>> +		if (count > msg_size) {
>> +			count -= msg_size;
>> +			tbuf += msg_size;
>> +		} else {
>> +			count = 0;
>> +		}
>> +	} while (count > 0);
>> +
>> +	return total;
>> +}
> Johan