Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758364AbbKSLOx (ORCPT ); Thu, 19 Nov 2015 06:14:53 -0500 Received: from mail-yk0-f170.google.com ([209.85.160.170]:32994 "EHLO mail-yk0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758230AbbKSLOr (ORCPT ); Thu, 19 Nov 2015 06:14:47 -0500 MIME-Version: 1.0 In-Reply-To: <564DA45A.9090800@hurleysoftware.com> References: <564C9A22.2060102@hurleysoftware.com> <564DA45A.9090800@hurleysoftware.com> Date: Thu, 19 Nov 2015 19:14:46 +0800 Message-ID: Subject: Re: [PATCH] usb: gadget: Add the console support for usb-to-serial port From: Baolin Wang To: Peter Hurley Cc: Felipe Balbi , Greg KH , r.baldyga@samsung.com, fabio.estevam@freescale.com, Philip Oberstaller , scottwood@freescale.com, Mark Brown , USB , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 16830 Lines: 569 On 19 November 2015 at 18:28, Peter Hurley wrote: > On 11/18/2015 09:35 PM, Baolin Wang wrote: >> On 18 November 2015 at 23:32, Peter Hurley wrote: >>> Hi Baolin, >>> >>> On 11/16/2015 02:05 AM, Baolin Wang wrote: >>>> It dose not work when we want to use the usb-to-serial port based >>>> on one usb gadget as a console. Thus this patch adds the console >>>> initialization to support this request. >>> >>> I have some high level concerns. >>> >>> 1. I would defer registering the console until the port has at least been >>> allocated in gserial_alloc_line(), and unregister when the line is freed. >>> That also reduces many of the conditions that you shouldn't need to >>> check, like port number range and so on. >> >> The 'setup' callback of 'struct console' is just do some memory >> allocation and member initialization, that no need to defer >> registering the console in gserial_alloc_line(). But the >> 'gs_console_connect()' which will use the port need to be called in >> gserial_connect(). > > My point here was why are you registering the console before the port > table is even allocated and initialized? The console can't possibly > perform i/o that early because the port doesn't even exist. > Which is why I suggested waiting until gserial_alloc_line() to > register the console. > > A typical console setup() performs the cross-reference linking between > the console data structure and the port table. The reason for that > is the console needs to be cleaned up if the port is being torn down. > > For example, in gserial_disconnect() the port->port_usb is reset to NULL, > and later in gserial_console_exit(): > > if (port && port->port_usb) { > .... > gs_request_free(req, ep); > } > > which means your leaking the request allocation when the port has been > disconnected. > Yeah, that's right. I'll defer the console registration until gserial_connect() and unregistration in disconnect. > >>> Further, consider deferring the console registration until gserial_connect(); >>> that would further simplify things. In this case, unregistration would >>> happen at disconnect. >> >> That sounds reasonable. I would try. >> >>> >>> 2. Why are you using a kworker for actual device i/o when all of the i/o >>> is done with interrupts disabled anyway? >>> Getting rid of the work would eliminate using the 8K intermediate buffer >>> as well. >> >> If remove the kworker, there are some deadlocks to call the printk() >> when in the process of transferring data with usb endpoint. So we need >> a async kworker to complete the io or it can not work. > > The commit log should detail the major design choices, including why you > used the kworker (because of re-entrancy issues with usb endpoint). > OK. > > >>> 3. If for some reason i/o deferral is really necessary, consider using a kthread >>> kworker instead of the pooled kworker. The scheduler response will be _way_ >>> better. >>> >> >> OK, make sense. >> >>> 4. If for some reason i/o deferral is really necessary, use a circular buffer >>> for the intermediate buffer, preferably lockless since there is only >>> one producer and one consumer. >>> >> >> Yeah, the circular buffer is better but more tricky. I would try. >> >>> Some other review comments below; please ignore anything other reviewers >>> have already noted. >>> >>> Regards, >>> Peter Hurley >>> >>>> Signed-off-by: Baolin Wang >>>> --- >>>> drivers/usb/gadget/Kconfig | 6 + >>>> drivers/usb/gadget/function/u_serial.c | 238 ++++++++++++++++++++++++++++++++ >>>> 2 files changed, 244 insertions(+) >>>> >>>> diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig >>>> index 33834aa..be5aab9 100644 >>>> --- a/drivers/usb/gadget/Kconfig >>>> +++ b/drivers/usb/gadget/Kconfig >>>> @@ -127,6 +127,12 @@ config USB_GADGET_STORAGE_NUM_BUFFERS >>>> a module parameter as well. >>>> If unsure, say 2. >>>> >>>> +config U_SERIAL_CONSOLE >>>> + bool "Serial gadget console support" >>>> + depends on USB_G_SERIAL >>>> + help >>>> + It supports the serial gadget can be used as a console. >>>> + >>>> source "drivers/usb/gadget/udc/Kconfig" >>>> >>>> # >>>> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c >>>> index f7771d8..4ade527 100644 >>>> --- a/drivers/usb/gadget/function/u_serial.c >>>> +++ b/drivers/usb/gadget/function/u_serial.c >>>> @@ -27,6 +27,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> #include "u_serial.h" >>>> >>>> @@ -79,6 +80,16 @@ >>>> */ >>>> #define QUEUE_SIZE 16 >>>> #define WRITE_BUF_SIZE 8192 /* TX only */ >>>> +#define GS_BUFFER_SIZE (4096) >>>> +#define GS_CONSOLE_BUF_SIZE (2 * GS_BUFFER_SIZE) >>>> + >>>> +struct gscons_info { >>>> + struct gs_port *port; >>>> + struct tty_driver *tty_driver; >>>> + struct work_struct work; >>>> + int buf_tail; >>>> + char buf[GS_CONSOLE_BUF_SIZE]; >>>> +}; >>> >>> Make struct gscons_info a static declaration instead of >>> allocating it. >> >> But I think the dynamic allocation is more reasonable with reducing >> some global variables. > > But introduces a failure mode that doesn't exist with the > static definition. > OK. I'll consider that. > >>>> /* circular buffer */ >>>> struct gs_buf { >>>> @@ -118,6 +129,7 @@ struct gs_port { >>>> >>>> /* REVISIT this state ... */ >>>> struct usb_cdc_line_coding port_line_coding; /* 8-N-1 etc */ >>>> + struct usb_request *console_req; >>>> }; >>>> >>>> static struct portmaster { >>>> @@ -1054,6 +1066,7 @@ gs_port_alloc(unsigned port_num, struct usb_cdc_line_coding *coding) >>>> >>>> port->port_num = port_num; >>>> port->port_line_coding = *coding; >>>> + port->console_req = NULL; >>>> >>>> ports[port_num].port = port; >>>> out: >>>> @@ -1143,6 +1156,227 @@ err: >>>> } >>>> EXPORT_SYMBOL_GPL(gserial_alloc_line); >>>> >>>> +#ifdef CONFIG_U_SERIAL_CONSOLE >>>> + >>>> +static struct usb_request *gs_request_new(struct usb_ep *ep, int buffer_size) >>> ^^^^^^^^^^^^^^^ >>> With only a single caller that uses a symbolic constant, is the >>> 'buffer_size' parameter necessary? >>> >> >> Yeah, I'll remove the 'buffer_size' parameter. >> >>> >>>> +{ >>>> + struct usb_request *req = usb_ep_alloc_request(ep, GFP_ATOMIC); >>>> + >>> >>> Remove this newline. >> >> OK. >> >>> >>>> + if (!req) >>>> + return NULL; >>>> + >>>> + /* now allocate buffers for the requests */ >>> >>> Unnecessary comment. >> >> OK. >> >>> >>>> + req->buf = kmalloc(buffer_size, GFP_ATOMIC); >>>> + if (!req->buf) { >>>> + usb_ep_free_request(ep, req); >>>> + return NULL; >>>> + } >>>> + >>>> + return req; >>>> +} >>>> + >>>> +static void gs_request_free(struct usb_request *req, struct usb_ep *ep) >>>> +{ >>>> + if (req) { >>>> + kfree(req->buf); >>>> + usb_ep_free_request(ep, req); >>>> + } >>>> +} >>>> + >>>> +static void gs_complete_out(struct usb_ep *ep, struct usb_request *req) >>>> +{ >>>> + if (req->status != 0 && req->status != -ECONNRESET) >>>> + return; >>>> +} >>>> + >>>> +static struct console gserial_cons; >>>> +static int gs_console_connect(void) >>> >>> Pass the console * as parameter, instead of forward declaring the console. >>> Or initialize info directly from the static struct gscons_info address. >> >> Make sense. >> >>> >>>> +{ >>>> + struct gscons_info *info = gserial_cons.data; >>>> + int port_num = gserial_cons.index; >>>> + struct usb_request *req; >>>> + struct gs_port *port; >>>> + struct usb_ep *ep; >>>> + >>>> + if (port_num >= MAX_U_SERIAL_PORTS || port_num < 0) { >>>> + pr_err("%s: port num [%d] exceeds the range.\n", >>>> + __func__, port_num); >>>> + return -ENXIO; >>>> + } >>>> + >>>> + port = ports[port_num].port; >>>> + if (!port) { >>>> + pr_err("%s: serial line [%d] not allocated.\n", >>>> + __func__, port_num); >>>> + return -ENODEV; >>>> + } >>>> + >>>> + if (!port->port_usb) { >>>> + pr_err("%s: no port usb.\n", __func__); >>>> + return -ENODEV; >>>> + } >>>> + >>>> + ep = port->port_usb->in; >>>> + if (!ep) { >>>> + pr_err("%s: no usb endpoint.\n", __func__); >>>> + return -ENXIO; >>>> + } >>> >>> Looking at the caller, gserial_connect(), none of the error >>> conditions above look possible. >> >> That's right. I'll remove these checks. >> >>> >>> >>>> + >>>> + req = port->console_req; >>>> + if (!req) { >>>> + req = gs_request_new(ep, GS_BUFFER_SIZE); >>> >>> Where is port->console_req assigned to? >> >> The connect may be called several times, if the req is allocated at >> one time, there is no need to assign it. > > You've missed my point: where is > > port->console_req = ????? Sorry, I missed here and will fix it. > > >>>> + if (!req) { >>>> + pr_err("%s: request fail.\n", __func__); >>> >>> Remove redundant error message; the allocator has already done so. >> >> OK. >> >>> >>>> + return -ENOMEM; >>>> + } >>>> + req->complete = gs_complete_out; >>>> + } >>>> + >>>> + info->port = port; >>>> + >>>> + pr_debug("%s: port[%d] console connect!\n", __func__, port_num); >>>> + return 0; >>>> +} >>>> + >>>> +static void gs_console_work(struct work_struct *work) >>>> +{ >>>> + struct gscons_info *info = container_of(work, struct gscons_info, work); >>>> + struct gs_port *port = info->port; >>>> + struct usb_request *req; >>>> + struct usb_ep *ep; >>>> + int xfer, ret, count; >>>> + char *p; >>>> + >>>> + if (!port || !port->port_usb) >>>> + return; >>>> + >>>> + req = port->console_req; >>>> + ep = port->port_usb->in; >>>> + if (!req || !ep) >>>> + return; >>>> + >>>> + spin_lock_irq(&port->port_lock); >>>> + count = info->buf_tail; >>>> + p = info->buf; >>>> + >>>> + while (count > 0 && !port->write_busy) { >>>> + if (count > GS_BUFFER_SIZE) >>>> + xfer = GS_BUFFER_SIZE; >>>> + else >>>> + xfer = count; >>>> + >>>> + memcpy(req->buf, p, xfer); >>>> + req->length = xfer; >>>> + >>>> + port->write_busy = true; >>>> + spin_unlock(&port->port_lock); >>>> + ret = usb_ep_queue(ep, req, GFP_ATOMIC); >>>> + spin_lock(&port->port_lock); >>>> + port->write_busy = false; >>>> + if (ret < 0) >>>> + break; >>>> + >>>> + p += xfer; >>>> + count -= xfer; >>>> + } >>>> + >>>> + info->buf_tail -= count; > > I'm not seeing how info->buf_tail is ever reset to 0. > > count = info->buf_tail > > while (count > 0) { > .... > count -= xfer; > } > > At loop exit count == 0, so > > info->buf_tail -= count; > > never decreases buf_tail? > Sorry, that's a mistake and I'll fix that. > >>>> + spin_unlock_irq(&port->port_lock); >>>> +} >>>> + >>>> +static int gs_console_setup(struct console *co, char *options) >>>> +{ >>>> + struct gscons_info *gscons_info; >>>> + >>>> + gscons_info = kzalloc(sizeof(struct gscons_info), GFP_KERNEL); >>>> + if (!gscons_info) >>>> + return -ENOMEM; >>>> + >>>> + gscons_info->port = NULL; >>> >>> Redundant. >> >> Will remove it. >> >>> >>>> + gscons_info->tty_driver = gs_tty_driver; >>>> + INIT_WORK(&gscons_info->work, gs_console_work); >>>> + gscons_info->buf_tail = 0; >>> >>> Redundant. >> >> Will remove it. >> >>> >>>> + co->data = gscons_info; >>>> + >>>> + return 0; >>>> +} >>>> + >>>> +static void gs_console_write(struct console *co, >>>> + const char *buf, unsigned count) >>>> +{ >>>> + struct gscons_info *info = co->data; >>>> + int avail, xfer; >>>> + char *p; >>>> + >>>> + avail = GS_CONSOLE_BUF_SIZE - info->buf_tail; >>>> + if (count > avail) >>>> + xfer = avail; >>>> + else >>>> + xfer = count; >>> >>> xfer = min(count, GS_CONSOLE_BUF_SIZE - info->buf_tail); >> >> Yeah, that's right. >> >>> >>>> + >>>> + p = &info->buf[info->buf_tail]; >>>> + memcpy(p, buf, xfer); >>>> + info->buf_tail += xfer; >>> >>> What is preventing concurrently running work and this from >>> using/modifying the info->buf and info->buf_tail simultaneously? >> >> Like I said above, it will meet deadlocks if running the work >> directly, then introduce the kworker. > > You've missed my point here: > > CPU 0 CPU 1 > -------------------------------- ------------------------------- > gs_console_write() gs_console_work() > > info->buf_tail += xfer info->buf_tail -= count; > > > Neither of these operations are atomic so what will the value of > info->buf_tail be? For example: > > A <= LOAD(info->buf_tail) > B <= LOAD(info->buf_tail) > A <= A + xfer B <= B - count > STORE(A, info->buf_tail) > STORE(B, info->buf_tail) > > The result is as if info->buf_tail += xfer never happened. > Make sense. I would remove the buffer counter and replace with a circular buffer. Very thanks for your good suggestions. > >>>> + >>>> + schedule_work(&info->work); >>>> +} >>>> + >>>> +static struct tty_driver *gs_console_device(struct console *co, int *index) >>>> +{ >>>> + struct gscons_info *info = co->data; >>>> + >>>> + *index = co->index; >>>> + return info->tty_driver; >>>> +} >>>> + >>>> +static struct console gserial_cons = { >>>> + .name = "ttyGS", >>>> + .write = gs_console_write, >>>> + .device = gs_console_device, >>>> + .setup = gs_console_setup, >>>> + .flags = CON_PRINTBUFFER, >>>> + .index = -1, >>>> +}; >>>> + >>>> +static void gserial_console_init(void) >>>> +{ >>>> + register_console(&gserial_cons); >>>> +} >>>> + >>>> +static void gserial_console_exit(void) >>>> +{ >>>> + struct gscons_info *info = gserial_cons.data; >>>> + struct gs_port *port = info->port; >>>> + struct usb_request *req; >>>> + struct usb_ep *ep; >>>> + >>>> + if (port && port->port_usb) { >>>> + req = port->console_req; >>>> + ep = port->port_usb->in; >>>> + gs_request_free(req, ep); >>>> + } >>>> + >>>> + kfree(info); >>>> + unregister_console(&gserial_cons); >>>> +} >>>> + >>>> +#else >>>> + >>>> +static int gs_console_connect(void) >>>> +{ >>>> + return 0; >>>> +} >>>> + >>>> +static void gserial_console_init(void) >>>> +{ >>>> +} >>>> + >>>> +static void gserial_console_exit(void) >>>> +{ >>>> +} >>>> + >>>> +#endif >>>> + >>>> /** >>>> * gserial_connect - notify TTY I/O glue that USB link is active >>>> * @gser: the function, set up with endpoints and descriptors >>>> @@ -1219,6 +1453,7 @@ int gserial_connect(struct gserial *gser, u8 port_num) >>>> gser->disconnect(gser); >>>> } >>>> >>>> + status = gs_console_connect(); >>>> spin_unlock_irqrestore(&port->port_lock, flags); >>>> >>>> return status; >>>> @@ -1320,6 +1555,8 @@ static int userial_init(void) >>>> goto fail; >>>> } >>>> >>>> + gserial_console_init(); >>>> + >>>> pr_debug("%s: registered %d ttyGS* device%s\n", __func__, >>>> MAX_U_SERIAL_PORTS, >>>> (MAX_U_SERIAL_PORTS == 1) ? "" : "s"); >>>> @@ -1334,6 +1571,7 @@ module_init(userial_init); >>>> >>>> static void userial_cleanup(void) >>>> { >>>> + gserial_console_exit(); >>>> tty_unregister_driver(gs_tty_driver); >>>> put_tty_driver(gs_tty_driver); >>>> gs_tty_driver = NULL; >>>> >>> >> >> >> > -- Baolin.wang Best Regards -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/