[PATCH 1/1] usb: cdc-ncm: Increase maximum allowed datagram size

[PATCH 1/1] usb: cdc-ncm: Increase maximum allowed datagram size

[Toby Gray]

Some NCM devices exist which will send datagrams larger than 2k and
don't support the GetMaxDatagramSize request, such as the Nokia 701
Mobile Telephone.

This sets the maximum limit of datagrams to the theoretical limit for
16-bit NTBs, preventing dropping of large datagrams received from some
devices.

Signed-off-by: Toby Gray <toby.gray-BiNz9QiKYoNBDgjK7y7TUQ@public.gmane.org>
---
 drivers/net/usb/cdc_ncm.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 3a539a9..d9be846 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -67,8 +67,10 @@
 
 #define	CDC_NCM_MIN_TX_PKT			512	/* bytes */
 
-/* Default value for MaxDatagramSize */
-#define	CDC_NCM_MAX_DATAGRAM_SIZE		2048	/* bytes */
+/* Maximum value for MaxDatagramSize, this is 16k (max NTB size)
+ * minus NTH size (12 bytes) and minus the smallest possible NDP size
+ * (16 bytes). */
+#define	CDC_NCM_MAX_DATAGRAM_SIZE		16356	/* bytes */
 
 /*
  * Maximum amount of datagrams in NCM Datagram Pointer Table, not counting
-- 
1.7.0.4

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Re: [PATCH 1/1] usb: cdc-ncm: Increase maximum allowed datagram size

[David Miller]

From: Toby Gray <toby.gray@realvnc.com>
Date: Tue, 14 Feb 2012 14:39:35 +0000

> Some NCM devices exist which will send datagrams larger than 2k and
> don't support the GetMaxDatagramSize request, such as the Nokia 701
> Mobile Telephone.
> 
> This sets the maximum limit of datagrams to the theoretical limit for
> 16-bit NTBs, preventing dropping of large datagrams received from some
> devices.
> 
> Signed-off-by: Toby Gray <toby.gray@realvnc.com>

Can a USB expert please sanity check this before I apply it?

Thanks.

Re: [PATCH 1/1] usb: cdc-ncm: Increase maximum allowed datagram size

[Alexey Orishko]

On Tue, Feb 14, 2012 at 8:46 PM, David Miller <davem@davemloft.net> wrote:
>
> Can a USB expert please sanity check this before I apply it?

I would recommend to change CDC_NCM_NTB_MAX_SIZE_TX(RX) to 32K and
simply set MAX_DATAGRAM_SIZE to 16K

/alexey

Re: [PATCH 1/1] usb: cdc-ncm: Increase maximum allowed datagram size

[Oliver Neukum]

Am Dienstag, 14. Februar 2012, 23:27:29 schrieb Alexey Orishko:
> On Tue, Feb 14, 2012 at 8:46 PM, David Miller <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org> wrote:
> >
> > Can a USB expert please sanity check this before I apply it?
> 
> I would recommend to change CDC_NCM_NTB_MAX_SIZE_TX(RX) to 32K and
> simply set MAX_DATAGRAM_SIZE to 16K

Have you tried that under severe memory presssure?

	Regards
		Oliver
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Re: [PATCH 1/1] usb: cdc-ncm: Increase maximum allowed datagram size

[Alexey Orishko]

On Wed, Feb 15, 2012 at 9:53 AM, Oliver Neukum <oneukum-l3A5Bk7waGM@public.gmane.org> wrote:
> Have you tried that under severe memory presssure?

Well, it is a simplistic view upon host configuration.
Developing of NCM spec was done with mind set, that host must be more
capable than device.

However, proposal above doesn't solve problem completely due to usbnet.
Currently I'm testing some improvements/fixes related to data handling
and driver latency with the plan to post it in the near future.

Regards,
Alexey
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