Re: [PATCH net-next v8 2/2] net: Add Qcom WWAN control driver

The MHI WWWAN control driver allows MHI QCOM-based modems to expose
different modem control protocols/ports via the WWAN framework, so that
userspace modem tools or daemon (e.g. ModemManager) can control WWAN
config and state (APN config, SMS, provider selection...). A QCOM-based
modem can expose one or several of the following protocols:
- AT: Well known AT commands interactive protocol (microcom, minicom...)
- MBIM: Mobile Broadband Interface Model (libmbim, mbimcli)
- QMI: QCOM MSM/Modem Interface (libqmi, qmicli)
- QCDM: QCOM Modem diagnostic interface (libqcdm)
- FIREHOSE: XML-based protocol for Modem firmware management
        (qmi-firmware-update)

Note that this patch is mostly a rework of the earlier MHI UCI
tentative that was a generic interface for accessing MHI bus from
userspace. As suggested, this new version is WWAN specific and is
dedicated to only expose channels used for controlling a modem, and
for which related opensource userpace support exist.

Signed-off-by: Loic Poulain <redacted>
---
 v2: update copyright (2021)
 v3: Move driver to dedicated drivers/net/wwan directory
 v4: Rework to use wwan framework instead of self cdev management
 v5: Fix errors/typos in Kconfig
 v6: - Move to new wwan interface, No need dedicated call to wwan_dev_create
     - Cleanup code (remove legacy from mhi_uci, unused defines/vars...)
     - Remove useless write_lock mutex
     - Add mhi_wwan_wait_writable and mhi_wwan_wait_dlqueue_lock_irq helpers
     - Rework locking
     - Add MHI_WWAN_TX_FULL flag
     - Add support for NONBLOCK read/write
 v7: Fix change log (mixed up 1/2 and 2/2)
 v8: - Implement wwan_port_ops (instead of fops)
     - Remove all mhi wwan data obsolete members (kref, lock, waitqueues)
     - Add tracking of RX buffer budget
     - Use WWAN TX flow control function to stop TX when MHI queue is full

 drivers/net/wwan/Kconfig         |  14 +++
 drivers/net/wwan/Makefile        |   2 +
 drivers/net/wwan/mhi_wwan_ctrl.c | 253 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 269 insertions(+)
 create mode 100644 drivers/net/wwan/mhi_wwan_ctrl.c

diff --git a/drivers/net/wwan/Kconfig b/drivers/net/wwan/Kconfig
index 545fe54..ce0bbfb 100644
--- a/drivers/net/wwan/Kconfig
+++ b/drivers/net/wwan/Kconfig

@@ -19,4 +19,18 @@ config WWAN_CORE
 	  To compile this driver as a module, choose M here: the module will be
 	  called wwan.
 
+config MHI_WWAN_CTRL
+	tristate "MHI WWAN control driver for QCOM-based PCIe modems"
+	select WWAN_CORE
+	depends on MHI_BUS
+	help
+	  MHI WWAN CTRL allows QCOM-based PCIe modems to expose different modem
+	  control protocols/ports to userspace, including AT, MBIM, QMI, DIAG
+	  and FIREHOSE. These protocols can be accessed directly from userspace
+	  (e.g. AT commands) or via libraries/tools (e.g. libmbim, libqmi,
+	  libqcdm...).
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called mhi_wwan_ctrl
+
 endif # WWAN

diff --git a/drivers/net/wwan/Makefile b/drivers/net/wwan/Makefile
index 934590b..556cd90 100644
--- a/drivers/net/wwan/Makefile
+++ b/drivers/net/wwan/Makefile

@@ -5,3 +5,5 @@
 
 obj-$(CONFIG_WWAN_CORE) += wwan.o
 wwan-objs += wwan_core.o
+
+obj-$(CONFIG_MHI_WWAN_CTRL) += mhi_wwan_ctrl.o

diff --git a/drivers/net/wwan/mhi_wwan_ctrl.c b/drivers/net/wwan/mhi_wwan_ctrl.c
new file mode 100644
index 0000000..f2fab23
--- /dev/null
+++ b/drivers/net/wwan/mhi_wwan_ctrl.c

@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2021, Linaro Ltd <loic.poulain@linaro.org> */
+#include <linux/kernel.h>
+#include <linux/mhi.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/wwan.h>
+
+/* MHI wwan flags */
+#define MHI_WWAN_DL_CAP		BIT(0)
+#define MHI_WWAN_UL_CAP		BIT(1)
+#define MHI_WWAN_STARTED	BIT(2)
+
+#define MHI_WWAN_MAX_MTU	0x8000
+
+struct mhi_wwan_dev {
+	/* Lower level is a mhi dev, upper level is a wwan port */
+	struct mhi_device *mhi_dev;
+	struct wwan_port *wwan_port;
+
+	/* State and capabilities */
+	unsigned long flags;
+	size_t mtu;
+
+	/* Protect against concurrent TX and TX-completion (bh) */
+	spinlock_t tx_lock;
+
+	struct work_struct rx_refill;
+	atomic_t rx_budget;