linux/drivers/usb
Oliver Neukum df3aa13c7b Revert "cdc-acm: implement put_char() and flush_chars()"
This reverts commit a81cf9799a.

The patch causes a regression, which I cannot find the reason for.
So let's revert for now, as a revert hurts only performance.

Original report:
I was trying to resolve the problem with Oliver but we don't get any conclusion
for 5 months, so I am now sending this to mail list and cdc_acm authors.

I am using simple request-response protocol to obtain the boiller parameters
in constant intervals.

A simple one transaction is:
1. opening the /dev/ttyACM0
2. sending the following 10-bytes request to the device:
   unsigned char req[] = {0x02, 0xfe, 0x01, 0x05, 0x08, 0x02, 0x01, 0x69, 0xab, 0x03};
3. reading response (frame of 74 bytes length).
4. closing the descriptor
I am doing this transaction with 5 seconds intervals.

Before the bad commit everything was working correctly: I've got a requests and
a responses in a timely manner.

After the bad commit more time I am using the kernel module, more problems I have.
The graph [2] is showing the problem.

As you can see after module load all seems fine but after about 30 minutes I've got
a plenty of EAGAINs when doing read()'s and trying to read back the data.

When I rmmod and insmod the cdc_acm module again, then the situation is starting
over again: running ok shortly after load, and more time it is running, more EAGAINs
I have when calling read().

As a bonus I can see the problem on the device itself:
The device is configured as you can see here on this screen [3].
It has two transmision LEDs: TX and RX. Blink duration is set for 100ms.
This is a recording before the bad commit when all is working fine: [4]
And this is with the bad commit: [5]
As you can see the TX led is blinking wrongly long (indicating transmission?)
and I have problems doing read() calls (EAGAIN).

Reported-by: Mariusz Bialonczyk <manio@skyboo.net>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Fixes: a81cf9799a ("cdc-acm: implement put_char() and flush_chars()")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-09-10 20:40:29 +02:00
..
atm USB: atm: fix up some remaining DEVICE_ATTR() usage 2018-01-24 08:49:52 +01:00
c67x00 USB: add SPDX identifiers to all remaining Makefiles 2017-11-07 15:53:48 +01:00
chipidea Merge 4.18-rc7 into usb-next 2018-07-30 10:04:58 +02:00
class Revert "cdc-acm: implement put_char() and flush_chars()" 2018-09-10 20:40:29 +02:00
common usb: Change usb_of_get_companion_dev() place to usb/common 2018-09-10 20:40:29 +02:00
core usb: Change usb_of_get_companion_dev() place to usb/common 2018-09-10 20:40:29 +02:00
dwc2 usb: dwc2: Fix call location of dwc2_check_core_endianness 2018-09-05 13:12:31 +03:00
dwc3 usb: fixes for v4.19-rc2 2018-09-06 11:21:54 +02:00
early usb: early: Correct the endpoint type value for bulk in endpoint 2017-12-07 16:03:15 +01:00
gadget usb: gadget: udc: renesas_usb3: fix maxpacket size of ep0 2018-08-29 10:00:30 +03:00
host usb: xhci: fix interrupt transfer error happened on MTK platforms 2018-09-10 20:40:29 +02:00
image USB/PHY patches for 4.15-rc1 2017-11-13 21:14:07 -08:00
isp1760 usb: isp1760: remove redundant variable 'selector' 2018-07-13 15:41:56 +02:00
misc usb: misc: uss720: Fix two sleep-in-atomic-context bugs 2018-09-05 14:36:53 +02:00
mon USB: mon: use ktime_get_real_ts64 instead of getnstimeofday64 2018-06-25 21:58:26 +08:00
mtu3 usb: mtu3: fix error of xhci port id when enable U3 dual role 2018-09-05 13:27:07 +02:00
musb USB: musb: mark expected switch fall-throughs 2018-07-02 18:08:19 +02:00
phy usb/phy: fix PPC64 build errors in phy-fsl-usb.c 2018-07-21 08:15:12 +02:00
renesas_usbhs usb: renesas_usbhs: Kconfig: convert to SPDX identifiers 2018-07-30 15:27:14 +02:00
roles usb: roles: intel_xhci: Enable runtime PM 2018-05-24 18:17:00 +02:00
serial USB: serial: ti_usb_3410_5052: fix array underflow in completion handler 2018-08-27 11:53:19 +02:00
storage usb: uas: add support for more quirk flags 2018-09-05 13:27:07 +02:00
typec usb/typec: fix kernel-doc notation warning for typec_match_altmode 2018-09-05 14:36:53 +02:00
usbip usb: usbip: remove redundant pointer ep 2018-07-13 15:41:55 +02:00
wusbcore usb: wusbcore: security: cast sizeof to int for comparison 2018-07-02 18:08:19 +02:00
Kconfig usb: select USB_COMMON for usb role switch config 2018-04-22 15:23:37 +02:00
Makefile usb: roles: Add Intel xHCI USB role switch driver 2018-03-22 13:49:27 +01:00
README
usb-skeleton.c usb: usb-skeleton: use irqsave() in USB's complete callback 2018-06-28 19:36:06 +09:00

To understand all the Linux-USB framework, you'll use these resources:

    * This source code.  This is necessarily an evolving work, and
      includes kerneldoc that should help you get a current overview.
      ("make pdfdocs", and then look at "usb.pdf" for host side and
      "gadget.pdf" for peripheral side.)  Also, Documentation/usb has
      more information.

    * The USB 2.0 specification (from www.usb.org), with supplements
      such as those for USB OTG and the various device classes.
      The USB specification has a good overview chapter, and USB
      peripherals conform to the widely known "Chapter 9".

    * Chip specifications for USB controllers.  Examples include
      host controllers (on PCs, servers, and more); peripheral
      controllers (in devices with Linux firmware, like printers or
      cell phones); and hard-wired peripherals like Ethernet adapters.

    * Specifications for other protocols implemented by USB peripheral
      functions.  Some are vendor-specific; others are vendor-neutral
      but just standardized outside of the www.usb.org team.

Here is a list of what each subdirectory here is, and what is contained in
them.

core/		- This is for the core USB host code, including the
		  usbfs files and the hub class driver ("hub_wq").

host/		- This is for USB host controller drivers.  This
		  includes UHCI, OHCI, EHCI, and others that might
		  be used with more specialized "embedded" systems.

gadget/		- This is for USB peripheral controller drivers and
		  the various gadget drivers which talk to them.


Individual USB driver directories.  A new driver should be added to the
first subdirectory in the list below that it fits into.

image/		- This is for still image drivers, like scanners or
		  digital cameras.
../input/	- This is for any driver that uses the input subsystem,
		  like keyboard, mice, touchscreens, tablets, etc.
../media/	- This is for multimedia drivers, like video cameras,
		  radios, and any other drivers that talk to the v4l
		  subsystem.
../net/		- This is for network drivers.
serial/		- This is for USB to serial drivers.
storage/	- This is for USB mass-storage drivers.
class/		- This is for all USB device drivers that do not fit
		  into any of the above categories, and work for a range
		  of USB Class specified devices. 
misc/		- This is for all USB device drivers that do not fit
		  into any of the above categories.