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

Greg KH
2021-04-02T14:05:55Z

On Fri, Apr 02, 2021 at 04:06:37PM +0200, Loic Poulain wrote:
> 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 <loic.poulain@linaro.org>
> ---
> 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;

Why is this atomic if you have a real lock already?

> +};
> +
> +static bool mhi_wwan_ctrl_refill_needed(struct mhi_wwan_dev *mhiwwan)
> +{
> + if (!test_bit(MHI_WWAN_STARTED, &mhiwwan->flags))
> + return false;
> +
> + if (!test_bit(MHI_WWAN_DL_CAP, &mhiwwan->flags))
> + return false;

What prevents these bits from being changed right after reading them?

> +
> + if (!atomic_read(&mhiwwan->rx_budget))
> + return false;

Why is this atomic? What happens if it changes right after returning?

This feels really odd.

> +
> + return true;
> +}
> +
> +void __mhi_skb_destructor(struct sk_buff *skb)
> +{
> + struct mhi_wwan_dev *mhiwwan = skb_shinfo(skb)->destructor_arg;
> +
> + /* RX buffer has been consumed, increase the allowed budget */
> + atomic_inc(&mhiwwan->rx_budget);

So this is a reference count? What is this thing?

> +
> + if (mhi_wwan_ctrl_refill_needed(mhiwwan))
> + schedule_work(&mhiwwan->rx_refill);

What if refill is needed right after this check? Did you just miss the
call?

> +static const struct mhi_device_id mhi_wwan_ctrl_match_table[] = {
> + { .chan = "DUN", .driver_data = WWAN_PORT_AT },
> + { .chan = "MBIM", .driver_data = WWAN_PORT_MBIM },
> + { .chan = "QMI", .driver_data = WWAN_PORT_QMI },
> + { .chan = "DIAG", .driver_data = WWAN_PORT_QCDM },
> + { .chan = "FIREHOSE", .driver_data = WWAN_PORT_FIREHOSE },

Wait, I thought these were all going to be separate somehow. Now they
are all muxed back together?

totally confused,

greg k-h