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From 2147c8ddfaa746cdb8857db070f907fa9abfcb60 Mon Sep 17 00:00:00 2001
From: Hiago De Franco <hiago.franco@toradex.com>
Date: Tue, 19 Dec 2023 11:52:07 -0300
Subject: [PATCH] usb: gadget: f_ncm: Apply workaround for packet clogging
The existing size of 32 is causing significant slowness and freezing when
utilizing the NCM protocol with a VNC client. This issue likely arises
because the VNC protocol relies on sending numerous small packets, which
accumulate until the 16KB limit is reached, leading to transmission
delays.
By decreasing TX_MAX_NUM_DPE to 4, we ensure that the NCM driver transmits
packets at a reduced interval, thereby resolving the VNC performance
issues. To comprehend how these packets are sent, refer to the code
snippet below from f_ncm.c:
```
/* If the new skb is too big for the current NCM NTB then
* set the current stored skb to be sent now and clear it
* ready for new data.
* NOTE: Assume maximum align for speed of calculation.
*/
if (ncm->skb_tx_data
&& (ncm->ndp_dgram_count >= TX_MAX_NUM_DPE
|| (ncm->skb_tx_data->len +
div + rem + skb->len +
ncm->skb_tx_ndp->len + ndp_align + (2 * dgram_idx_len))
> max_size)) {
skb2 = package_for_tx(ncm);
if (!skb2)
goto err;
}
```
This issue is presently under investigation on the Linux kernel mailing
list, and you can find the entire discussion at [1].
[1] https://lore.kernel.org/all/20231204183751.64202-1-hiagofranco@gmail.com/
Upstream-Status: Inappropriate [other]
There is no proper patch for now, so instead we're using this patch that
makes VNC work again as a temporarily solution until the mainline code
gets fixed.
Related-to: TEI-1078
Signed-off-by: Hiago De Franco <hiago.franco@toradex.com>
Signed-off-by: Joao Paulo Goncalves <joao.goncalves@toradex.com>
---
drivers/usb/gadget/function/f_ncm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index e0c183234283..5e972d1c1a0c 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -113,7 +113,7 @@ static inline unsigned ncm_bitrate(struct usb_gadget *g)
* Smaller packets are not likely to be trying to maximize the
* throughput and will be mstly sending smaller infrequent frames.
*/
-#define TX_MAX_NUM_DPE 32
+#define TX_MAX_NUM_DPE 4
/* Delay for the transmit to wait before sending an unfilled NTB frame. */
#define TX_TIMEOUT_NSECS 300000
--
2.34.1
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