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    SubjectRe: [PATCH v4 14/14] tty: gunyah: Add tty console driver for RM Console Services
    On Wed, Sep 28, 2022 at 12:56:33PM -0700, Elliot Berman wrote:
    > Gunyah provides a console for each VM using the VM console resource
    > manager APIs. This driver allows console data from other
    > VMs to be accessed via a TTY device and exports a console device to dump
    > Linux's own logs to our console.
    >
    > Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
    > ---
    > MAINTAINERS | 1 +
    > drivers/tty/Kconfig | 8 +
    > drivers/tty/Makefile | 1 +
    > drivers/tty/gunyah_tty.c | 409 +++++++++++++++++++++++++++++++++++++++
    > 4 files changed, 419 insertions(+)
    > create mode 100644 drivers/tty/gunyah_tty.c
    >
    > diff --git a/MAINTAINERS b/MAINTAINERS
    > index a0cba618e5f6..e8d4a6d9491a 100644
    > --- a/MAINTAINERS
    > +++ b/MAINTAINERS
    > @@ -8890,6 +8890,7 @@ F: Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
    > F: Documentation/virt/gunyah/
    > F: arch/arm64/gunyah/
    > F: drivers/mailbox/gunyah-msgq.c
    > +F: drivers/tty/gunyah_tty.c
    > F: drivers/virt/gunyah/
    > F: include/asm-generic/gunyah.h
    > F: include/linux/gunyah*.h
    > diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
    > index cc30ff93e2e4..ff86e977f9ac 100644
    > --- a/drivers/tty/Kconfig
    > +++ b/drivers/tty/Kconfig
    > @@ -380,6 +380,14 @@ config RPMSG_TTY
    > To compile this driver as a module, choose M here: the module will be
    > called rpmsg_tty.
    >
    > +config GUNYAH_CONSOLE
    > + tristate "Gunyah Consoles"
    > + depends on GUNYAH
    > + help
    > + This enables support for console output using Gunyah's Resource Manager RPC.
    > + This is normally used when a secondary VM which does not have exclusive access
    > + to a real or virtualized serial device and virtio-console is unavailable.

    module name?

    > +
    > endif # TTY
    >
    > source "drivers/tty/serdev/Kconfig"
    > diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
    > index 07aca5184a55..d183fbfd835b 100644
    > --- a/drivers/tty/Makefile
    > +++ b/drivers/tty/Makefile
    > @@ -27,5 +27,6 @@ obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o
    > obj-$(CONFIG_MIPS_EJTAG_FDC_TTY) += mips_ejtag_fdc.o
    > obj-$(CONFIG_VCC) += vcc.o
    > obj-$(CONFIG_RPMSG_TTY) += rpmsg_tty.o
    > +obj-$(CONFIG_GUNYAH_CONSOLE) += gunyah_tty.o
    >
    > obj-y += ipwireless/
    > diff --git a/drivers/tty/gunyah_tty.c b/drivers/tty/gunyah_tty.c
    > new file mode 100644
    > index 000000000000..80a20da11ad0
    > --- /dev/null
    > +++ b/drivers/tty/gunyah_tty.c
    > @@ -0,0 +1,409 @@
    > +// SPDX-License-Identifier: GPL-2.0-only
    > +/*
    > + * Copyright (c) 2022 Qualcomm Innovation Center, Inc. All rights reserved.
    > + */
    > +
    > +#define pr_fmt(fmt) "gh_rsc_mgr_console: " fmt

    You are a driver, use dev_printk() functions, no need for pr_fmt() at
    all, right?

    > +
    > +#include <linux/gunyah_rsc_mgr.h>
    > +#include <linux/auxiliary_bus.h>
    > +#include <linux/workqueue.h>
    > +#include <linux/spinlock.h>
    > +#include <linux/tty_flip.h>
    > +#include <linux/console.h>
    > +#include <linux/module.h>
    > +#include <linux/kfifo.h>
    > +#include <linux/kref.h>
    > +#include <linux/slab.h>
    > +#include <linux/tty.h>
    > +
    > +/*
    > + * The Linux TTY code does not support dynamic addition of tty derived devices so we need to know
    > + * how many tty devices we might need when space is allocated for the tty device. Since VMs might be
    > + * added/removed dynamically, we need to make sure we have enough allocated.

    Wrap comments at 80 columns please.

    > + */
    > +#define RSC_MGR_TTY_ADAPTERS 16

    We can have dynamic tty devices, so I don't understand this comment.
    What really is the problem here?

    > +
    > +/* # of payload bytes that can fit in a 1-fragment CONSOLE_WRITE message */
    > +#define RM_CONS_WRITE_MSG_SIZE ((1 * (GH_MSGQ_MAX_MSG_SIZE - 8)) - 4)
    > +
    > +struct rm_cons_port {
    > + struct tty_port port;
    > + u16 vmid;
    > + bool open;

    Why do you care if it is open or not?

    > + unsigned int index;
    > +
    > + DECLARE_KFIFO(put_fifo, char, 1024);
    > + spinlock_t fifo_lock;
    > + struct work_struct put_work;
    > +
    > + struct rm_cons_data *cons_data;
    > +};
    > +
    > +struct rm_cons_data {
    > + struct tty_driver *tty_driver;
    > + struct device *dev;
    > +
    > + spinlock_t ports_lock;
    > + struct rm_cons_port *ports[RSC_MGR_TTY_ADAPTERS];
    > +
    > + struct notifier_block rsc_mgr_notif;
    > + struct console console;
    > +};
    > +
    > +static void put_work_fn(struct work_struct *ws)
    > +{
    > + char buf[RM_CONS_WRITE_MSG_SIZE];
    > + int count, ret;
    > + struct rm_cons_port *port = container_of(ws, struct rm_cons_port, put_work);
    > +
    > + while (!kfifo_is_empty(&port->put_fifo)) {
    > + count = kfifo_out_spinlocked(&port->put_fifo, buf, sizeof(buf), &port->fifo_lock);
    > + if (count <= 0)
    > + continue;
    > +
    > + ret = gh_rm_console_write(port->vmid, buf, count);
    > + if (ret) {
    > + pr_warn_once("failed to send characters: %d\n", ret);

    What will this warning help with?

    > + break;

    If an error happens, shouldn't you keep trying to send the rest of the
    data?

    > + }
    > + }
    > +}
    > +
    > +static int rsc_mgr_console_notif(struct notifier_block *nb, unsigned long cmd, void *data)
    > +{
    > + int count, i;
    > + struct rm_cons_port *rm_port = NULL;
    > + struct tty_port *tty_port = NULL;
    > + struct rm_cons_data *cons_data = container_of(nb, struct rm_cons_data, rsc_mgr_notif);
    > + const struct gh_rm_notification *notif = data;
    > + struct gh_rm_notif_vm_console_chars const * const msg = notif->buff;
    > +
    > + if (cmd != GH_RM_NOTIF_VM_CONSOLE_CHARS ||
    > + notif->size < sizeof(*msg))
    > + return NOTIFY_DONE;
    > +
    > + spin_lock(&cons_data->ports_lock);
    > + for (i = 0; i < RSC_MGR_TTY_ADAPTERS; i++) {
    > + if (!cons_data->ports[i])
    > + continue;
    > + if (cons_data->ports[i]->vmid == msg->vmid) {
    > + rm_port = cons_data->ports[i];
    > + break;
    > + }
    > + }
    > + if (rm_port)
    > + tty_port = tty_port_get(&rm_port->port);
    > + spin_unlock(&cons_data->ports_lock);
    > +
    > + if (!rm_port)
    > + pr_warn("Received unexpected console characters for VMID %u\n", msg->vmid);
    > + if (!tty_port)
    > + return NOTIFY_DONE;
    > +
    > + count = tty_buffer_request_room(tty_port, msg->num_bytes);
    > + tty_insert_flip_string(tty_port, msg->bytes, count);
    > + tty_flip_buffer_push(tty_port);
    > +
    > + tty_port_put(tty_port);
    > + return NOTIFY_OK;
    > +}
    > +
    > +static ssize_t vmid_show(struct device *dev, struct device_attribute *attr, char *buf)
    > +{
    > + struct rm_cons_port *rm_port = dev_get_drvdata(dev);
    > +
    > + if (rm_port->vmid == GH_VMID_SELF)
    > + return sysfs_emit(buf, "self\n");
    > +
    > + return sysfs_emit(buf, "%u\n", rm_port->vmid);

    You didn't document this sysfs file, why not?

    And tty drivers should not have random sysfs files, please don't add
    this.

    > +}
    > +
    > +static DEVICE_ATTR_RO(vmid);
    > +
    > +static struct attribute *rsc_mgr_tty_dev_attrs[] = {
    > + &dev_attr_vmid.attr,
    > + NULL
    > +};
    > +
    > +static const struct attribute_group rsc_mgr_tty_dev_attr_group = {
    > + .attrs = rsc_mgr_tty_dev_attrs,
    > +};
    > +
    > +static const struct attribute_group *rsc_mgr_tty_dev_attr_groups[] = {
    > + &rsc_mgr_tty_dev_attr_group,
    > + NULL
    > +};
    > +
    > +static int rsc_mgr_tty_open(struct tty_struct *tty, struct file *filp)
    > +{
    > + int ret;
    > + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
    > +
    > + if (!rm_port->open) {

    Why are you caring if the port is open already or not?

    > + ret = gh_rm_console_open(rm_port->vmid);

    Can't this just be called for every open()?

    And what happens if this changes right after it is checked?

    > + if (ret) {
    > + pr_err("Failed to open RM console for vmid %x: %d\n", rm_port->vmid, ret);

    dev_err()

    > + return ret;
    > + }
    > + rm_port->open = true;
    > + }
    > +
    > + return tty_port_open(&rm_port->port, tty, filp);
    > +}
    > +
    > +static void rsc_mgr_tty_close(struct tty_struct *tty, struct file *filp)
    > +{
    > + int ret;
    > + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
    > +
    > + if (rm_port->open) {
    > + if (rm_port->vmid != GH_VMID_SELF) {
    > + ret = gh_rm_console_close(rm_port->vmid);
    > + if (ret)
    > + pr_warn("Failed to close RM console for vmid %d: %d\n",
    > + rm_port->vmid, ret);
    > + }
    > + rm_port->open = false;

    So if you had multiple open/close this would close the console the first
    close call, but not the second?

    Are you sure you tested this out properly?

    > +
    > + tty_port_close(&rm_port->port, tty, filp);
    > + }
    > +
    > +}
    > +
    > +static int rsc_mgr_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
    > +{
    > + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
    > + int ret;
    > +
    > + ret = kfifo_in_spinlocked(&rm_port->put_fifo, buf, count, &rm_port->fifo_lock);
    > + if (ret > 0)
    > + schedule_work(&rm_port->put_work);

    Why not just do the write here? Why is a work queue needed?

    > +
    > + return ret;
    > +}
    > +
    > +static unsigned int rsc_mgr_mgr_tty_write_room(struct tty_struct *tty)
    > +{
    > + struct rm_cons_port *rm_port = dev_get_drvdata(tty->dev);
    > +
    > + return kfifo_avail(&rm_port->put_fifo);
    > +}
    > +
    > +static void rsc_mgr_console_write(struct console *co, const char *buf, unsigned count)
    > +{
    > + struct rm_cons_port *rm_port = co->data;
    > + int ret;
    > +
    > + ret = kfifo_in_spinlocked(&rm_port->put_fifo, buf, count, &rm_port->fifo_lock);
    > + if (ret > 0)
    > + schedule_work(&rm_port->put_work);

    Same here, why not just send the data now?

    > +}
    > +
    > +static struct tty_driver *rsc_mgr_console_device(struct console *co, int *index)
    > +{
    > + struct rm_cons_port *rm_port = co->data;
    > +
    > + *index = rm_port->index;
    > + return rm_port->port.tty->driver;

    Love the locking :(

    > +}
    > +
    > +static int rsc_mgr_console_setup(struct console *co, char *unused)
    > +{
    > + int ret;
    > + struct rm_cons_port *rm_port = co->data;
    > +
    > + if (!rm_port->open) {
    > + ret = gh_rm_console_open(rm_port->vmid);
    > + if (ret) {
    > + pr_err("Failed to open RM console for vmid %x: %d\n", rm_port->vmid, ret);
    > + return ret;
    > + }
    > + rm_port->open = true;

    Again, don't mess with open/close.

    > + }
    > +
    > + return 0;
    > +}
    > +
    > +static int rsc_mgr_console_exit(struct console *co)
    > +{
    > + int ret;
    > + struct rm_cons_port *rm_port = co->data;
    > +
    > + if (rm_port->open) {
    > + ret = gh_rm_console_close(rm_port->vmid);
    > + if (ret) {
    > + pr_err("Failed to close RM console for vmid %x: %d\n", rm_port->vmid, ret);
    > + return ret;
    > + }
    > + rm_port->open = false;
    > + }
    > +
    > + return 0;
    > +}
    > +
    > +static const struct tty_operations rsc_mgr_tty_ops = {
    > + .open = rsc_mgr_tty_open,
    > + .close = rsc_mgr_tty_close,
    > + .write = rsc_mgr_tty_write,
    > + .write_room = rsc_mgr_mgr_tty_write_room,
    > +};
    > +
    > +static void rsc_mgr_port_destruct(struct tty_port *port)
    > +{
    > + struct rm_cons_port *rm_port = container_of(port, struct rm_cons_port, port);
    > + struct rm_cons_data *cons_data = rm_port->cons_data;
    > +
    > + spin_lock(&cons_data->ports_lock);
    > + WARN_ON(cons_data->ports[rm_port->index] != rm_port);

    Does this mean you just crashed the system if something went wrong?

    How can this ever happen?


    > + cons_data->ports[rm_port->index] = NULL;
    > + spin_unlock(&cons_data->ports_lock);
    > + kfree(rm_port);
    > +}
    > +
    > +static const struct tty_port_operations rsc_mgr_port_ops = {
    > + .destruct = rsc_mgr_port_destruct,
    > +};
    > +
    > +static struct rm_cons_port *rsc_mgr_port_create(struct rm_cons_data *cons_data, u16 vmid)
    > +{
    > + struct rm_cons_port *rm_port;
    > + struct device *ttydev;
    > + unsigned int index;
    > + int ret;
    > +
    > + rm_port = kzalloc(sizeof(*rm_port), GFP_KERNEL);
    > + rm_port->vmid = vmid;
    > + INIT_KFIFO(rm_port->put_fifo);
    > + spin_lock_init(&rm_port->fifo_lock);
    > + INIT_WORK(&rm_port->put_work, put_work_fn);
    > + tty_port_init(&rm_port->port);
    > + rm_port->port.ops = &rsc_mgr_port_ops;
    > +
    > + spin_lock(&cons_data->ports_lock);
    > + for (index = 0; index < RSC_MGR_TTY_ADAPTERS; index++) {
    > + if (!cons_data->ports[index]) {
    > + cons_data->ports[index] = rm_port;
    > + rm_port->index = index;
    > + break;
    > + }
    > + }
    > + spin_unlock(&cons_data->ports_lock);
    > + if (index >= RSC_MGR_TTY_ADAPTERS) {
    > + ret = -ENOSPC;
    > + goto err_put_port;
    > + }
    > +
    > + ttydev = tty_port_register_device_attr(&rm_port->port, cons_data->tty_driver, index,
    > + cons_data->dev, rm_port, rsc_mgr_tty_dev_attr_groups);
    > + if (IS_ERR(ttydev)) {
    > + ret = PTR_ERR(ttydev);
    > + goto err_put_port;
    > + }
    > +
    > + return rm_port;
    > +err_put_port:
    > + tty_port_put(&rm_port->port);
    > + return ERR_PTR(ret);
    > +}
    > +
    > +static int rsc_mgr_console_probe(struct auxiliary_device *auxdev,
    > + const struct auxiliary_device_id *aux_dev_id)
    > +{
    > + struct rm_cons_data *cons_data;
    > + struct rm_cons_port *rm_port;
    > + int ret;
    > + u16 vmid;
    > +
    > + cons_data = devm_kzalloc(&auxdev->dev, sizeof(*cons_data), GFP_KERNEL);
    > + if (!cons_data)
    > + return -ENOMEM;
    > + dev_set_drvdata(&auxdev->dev, cons_data);
    > + cons_data->dev = &auxdev->dev;
    > +
    > + cons_data->tty_driver = tty_alloc_driver(RSC_MGR_TTY_ADAPTERS,
    > + TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV);
    > + if (IS_ERR(cons_data->tty_driver))
    > + return PTR_ERR(cons_data->tty_driver);
    > +
    > + cons_data->tty_driver->driver_name = "gh";
    > + cons_data->tty_driver->name = "ttyGH";

    Where did you pick this name from?

    Where is it documented?

    > + cons_data->tty_driver->type = TTY_DRIVER_TYPE_SYSTEM;
    > + cons_data->tty_driver->init_termios = tty_std_termios;
    > + tty_set_operations(cons_data->tty_driver, &rsc_mgr_tty_ops);
    > +
    > + ret = tty_register_driver(cons_data->tty_driver);
    > + if (ret) {
    > + dev_err(&auxdev->dev, "Could not register tty driver: %d\n", ret);
    > + goto err_put_tty;
    > + }
    > +
    > + spin_lock_init(&cons_data->ports_lock);
    > +
    > + cons_data->rsc_mgr_notif.notifier_call = rsc_mgr_console_notif;
    > + ret = gh_rm_register_notifier(&cons_data->rsc_mgr_notif);
    > + if (ret) {
    > + dev_err(&auxdev->dev, "Could not register for resource manager notifications: %d\n",
    > + ret);
    > + goto err_put_tty;
    > + }
    > +
    > + rm_port = rsc_mgr_port_create(cons_data, GH_VMID_SELF);
    > + if (IS_ERR(rm_port)) {
    > + ret = PTR_ERR(rm_port);
    > + dev_err(&auxdev->dev, "Could not create own console: %d\n", ret);
    > + goto err_unreg_notif;
    > + }
    > +
    > + strncpy(cons_data->console.name, "ttyGH", sizeof(cons_data->console.name));

    Again, where did this name come from?

    thanks,

    greg k-h

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