Re: Usb serial driver change question in the linux kernel

[Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Sun, Feb 15, 2015 at 12:43:51AM +0000, Li, Elvin wrote:
> Hi All,
>                 I am using usb_debug driver in Linux kernel  to manage
>                 Ajays USB debug device (Vendor Id: 0525 Product Id:
>                 127a) which follows EHCI debug device specification.
>                 drivers\usb\serial\usb_debug.c was developed by Greg
>                 Kroah-Hartman, it worked very well with Ajays debug
>                 device until one change to usb-serial.c. I could see
>                 the Johan's change at
>                 https://github.com/torvalds/linux/commit/5083fd7bdfe6760577235a724cf6dccae13652c2.

> Does anyone has ideas how the issue could be resolved?

Thanks for the report. The commit mentioned above should simply be
reverted; a bulk-out buffer size smaller than the end-point size is
indeed valid.

Could you verify that the patch below fixes the issues you're seeing?

Thanks,
Johan


>From fffe54908863974c20adf1b1bf4e24e35a8d921b Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Date: Sun, 15 Feb 2015 11:57:53 +0700
Subject: [PATCH] Revert "USB: serial: make bulk_out_size a lower limit"

This reverts commit 5083fd7bdfe6760577235a724cf6dccae13652c2.

A bulk-out size smaller than the end-point size is indeed valid. The
offending commit broke the usb-debug driver for EHCI debug devices,
which use 8-byte buffers.

Fixes: 5083fd7bdfe6 ("USB: serial: make bulk_out_size a lower limit")
Reported-by: "Li, Elvin" <elvin.li-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: stable <stable-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>	# v3.15
Signed-off-by: Johan Hovold <johan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 drivers/usb/serial/usb-serial.c | 5 +++--
 include/linux/usb/serial.h      | 3 +--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 475723c006f9..19842370a07f 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -940,8 +940,9 @@ static int usb_serial_probe(struct usb_interface *interface,
 		port = serial->port[i];
 		if (kfifo_alloc(&port->write_fifo, PAGE_SIZE, GFP_KERNEL))
 			goto probe_error;
-		buffer_size = max_t(int, serial->type->bulk_out_size,
-						usb_endpoint_maxp(endpoint));
+		buffer_size = serial->type->bulk_out_size;
+		if (!buffer_size)
+			buffer_size = usb_endpoint_maxp(endpoint);
 		port->bulk_out_size = buffer_size;
 		port->bulk_out_endpointAddress = endpoint->bEndpointAddress;
 
diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 9bb547c7bce7..704a1ab8240c 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -190,8 +190,7 @@ static inline void usb_set_serial_data(struct usb_serial *serial, void *data)
  * @num_ports: the number of different ports this device will have.
  * @bulk_in_size: minimum number of bytes to allocate for bulk-in buffer
  *	(0 = end-point size)
- * @bulk_out_size: minimum number of bytes to allocate for bulk-out buffer
- *	(0 = end-point size)
+ * @bulk_out_size: bytes to allocate for bulk-out buffer (0 = end-point size)
  * @calc_num_ports: pointer to a function to determine how many ports this
  *	device has dynamically.  It will be called after the probe()
  *	callback is called, but before attach()
-- 
2.0.5

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