net: wwan: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect chinfo.name to be NUL-terminated based on its use with format
strings and sprintf:
rpmsg/rpmsg_char.c
165: dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
368: return sprintf(buf, "%s\n", eptdev->chinfo.name);

... and with strcmp():
| static struct rpmsg_endpoint *qcom_glink_create_ept(struct rpmsg_device *rpdev,
| rpmsg_rx_cb_t cb,
| void *priv,
| struct rpmsg_channel_info
| chinfo)
| ...
| const char *name = chinfo.name;
| ...
| if (!strcmp(channel->name, name))

Since chinfo is initialized as such (just above the strscpy()):

| struct rpmsg_channel_info chinfo = {
| .src = rpwwan->rpdev->src,
| .dst = RPMSG_ADDR_ANY,
| };

... we know other members are zero-initialized. This means no
NUL-padding is required (as any NUL-byte assignments are redundant).

Considering the above, a suitable replacement is `strscpy` due to the
fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231019-strncpy-drivers-net-wwan-rpmsg_wwan_ctrl-c-v2-1-ecf9b5a39430@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: wwan: Expose secondary AT port on DATA1

Our use-case needs two AT ports available:
One for running a ppp daemon, and another one for management

This patch enables a second AT port on DATA1

Signed-off-by: Jaime Breva <jbreva@nayarsystems.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

wwan: core: Support slicing in port TX flow of WWAN subsystem

wwan_port_fops_write inputs the SKB parameter to the TX callback of
the WWAN device driver. However, the WWAN device (e.g., t7xx) may
have an MTU less than the size of SKB, causing the TX buffer to be
sliced and copied once more in the WWAN device driver.

This patch implements the slicing in the WWAN subsystem and gives
the WWAN devices driver the option to slice(by frag_len) or not. By
doing so, the additional memory copy is reduced.

Meanwhile, this patch gives WWAN devices driver the option to reserve
headroom in fragments for the device-specific metadata.

Signed-off-by: haozhe chang <haozhe.chang@mediatek.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Link: https://lore.kernel.org/r/20230316095826.181904-1-haozhe.chang@mediatek.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net: wwan: Allow WWAN drivers to provide blocking tx and poll function

At the moment, the WWAN core provides wwan_port_txon/off() to implement
blocking writes. The tx() port operation should not block, instead
wwan_port_txon/off() should be called when the TX queue is full or has
free space again.

However, in some cases it is not straightforward to make use of that
functionality. For example, the RPMSG API used by rpmsg_wwan_ctrl.c
does not provide any way to be notified when the TX queue has space
again. Instead, it only provides the following operations:

- rpmsg_send(): blocking write (wait until there is space)
- rpmsg_trysend(): non-blocking write (return error if no space)
- rpmsg_poll(): set poll flags depending on TX queue state

Generally that's totally sufficient for implementing a char device,
but it does not fit well to the currently provided WWAN port ops.

Most of the time, using the non-blocking rpmsg_trysend() in the
WWAN tx() port operation works just fine. However, with high-frequent
writes to the char device it is possible to trigger a situation
where this causes issues. For example, consider the following
(somewhat unrealistic) example:

# dd if=/dev/zero bs=1000 of=/dev/wwan0qmi0
dd: error writing '/dev/wwan0qmi0': Resource temporarily unavailable
1+0 records out

This fails immediately after writing the first record. It's likely
only a matter of time until this triggers issues for some real application
(e.g. ModemManager sending a lot of large QMI packets).

The rpmsg_char device does not have this problem, because it uses
rpmsg_trysend() and rpmsg_poll() to support non-blocking operations.
Make it possible to use the same in the RPMSG WWAN driver by adding
two new optional wwan_port_ops:

- tx_blocking(): send data blocking if allowed
- tx_poll(): set additional TX poll flags

This integrates nicely with the RPMSG API and does not require
any change in existing WWAN drivers.

With these changes, the dd example above blocks instead of exiting
with an error.

Cc: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: wwan: Add RPMSG WWAN CTRL driver

The remote processor messaging (rpmsg) subsystem provides an interface
to communicate with other remote processors. On many Qualcomm SoCs this
is used to communicate with an integrated modem DSP that implements most
of the modem functionality and provides high-level protocols like
QMI or AT to allow controlling the modem.

For QMI, most older Qualcomm SoCs (e.g. MSM8916/MSM8974) have
a standalone "DATA5_CNTL" channel that allows exchanging QMI messages.
Note that newer SoCs (e.g. SDM845) only allow exchanging QMI messages
via a shared QRTR channel that is available via a socket API on Linux.

For AT, the "DATA4" channel accepts at least a limited set of AT
commands, on many older and newer Qualcomm SoCs, although QMI is
typically the preferred control protocol.

Often there are additional QMI/AT channels (usually named DATA*_CNTL
for QMI and DATA* for AT), but it is not clear if those are really
functional on all devices. Also, at the moment there is no use case
for having multiple QMI/AT ports. If needed more channels could be
added later after more testing.

Note that the data path (network interface) is entirely separate
from the control path and varies between Qualcomm SoCs, e.g. "IPA"
on newer Qualcomm SoCs or "BAM-DMUX" on some older ones.

The RPMSG WWAN CTRL driver exposes the QMI/AT control ports via the
WWAN subsystem, and therefore allows userspace like ModemManager to
set up the modem. Until now, ModemManager had to use the RPMSG-specific
rpmsg-char where the channels must be explicitly exposed as a char
device first and don't show up directly in sysfs.

The driver is a fairly simple glue layer between WWAN and RPMSG
and is mostly based on the existing mhi_wwan_ctrl.c and rpmsg_char.c.

Cc: Loic Poulain <loic.poulain@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: David S. Miller <davem@davemloft.net>