linux-kernel - [PATCH] g_serial: append zlp when tx buffer becomes empty

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Message-Id: <1243508004-17898-1-git-send-email-dg@emlix.com>
Date:	Thu, 28 May 2009 12:53:24 +0200
From:	Daniel Glöckner <dg@...ix.com>
To:	David Brownell <dbrownell@...rs.sourceforge.net>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Glöckner <dg@...ix.com>
Subject: [PATCH] g_serial: append zlp when tx buffer becomes empty

Some usb serial host drivers expect a short packet before they forward
the data to the application. This is caused by them trying to read more
than one packet at a time. So when the gadget sends an exact multiple
of the maximum packet size, it should append a zero-length packet.

Signed-off-by: Daniel Glöckner <dg@...ix.com>
---
 drivers/usb/gadget/u_serial.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/drivers/usb/gadget/u_serial.c b/drivers/usb/gadget/u_serial.c
index 3df70e5..f121030 100644
--- a/drivers/usb/gadget/u_serial.c
+++ b/drivers/usb/gadget/u_serial.c
@@ -372,6 +372,7 @@ __acquires(&port->port_lock)
 
 		req->length = len;
 		list_del(&req->list);
+		req->zero = (gs_buf_data_avail(&port->port_write_buf) == 0);
 
 		pr_vdebug(PREFIX "%d: tx len=%d, 0x%02x 0x%02x 0x%02x ...\n",
 				port->port_num, len, *((u8 *)req->buf),
-- 
1.6.1.3

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