net: thunder: change q_len's type to handle max ring size

The Cavium thunder nicvf driver supports rx/tx rings of up to 65536 entries per.
The number of entires are stored in the q_len member of struct q_desc_mem. The
problem is that q_len being a u16, results in 65536 becoming 0.

In getting pointers to descriptors in the rings, the driver uses q_len minus 1
as a mask after incrementing the pointer, in order to go back to the beginning
and not go past the end of the ring.

With the q_len set to 0 the mask is no longer correct and the driver does go
beyond the end of the ring, causing various ills. Usually the first thing that
shows up is a "NETDEV WATCHDOG: enP2p1s0f1 (nicvf): transmit queue 7 timed out"
warning.

This patch remedies the problem by changing q_len to a u32.

Signed-off-by: Dean Nelson <redacted>
---
 drivers/net/ethernet/cavium/thunder/nicvf_queues.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_queues.h b/drivers/net/ethernet/cavium/thunder/nicvf_queues.h
index 7d1e4e2aaad0..ce1eed7a6d63 100644
--- a/drivers/net/ethernet/cavium/thunder/nicvf_queues.h
+++ b/drivers/net/ethernet/cavium/thunder/nicvf_queues.h

@@ -213,7 +213,7 @@ struct rx_tx_queue_stats {
 struct q_desc_mem {
 	dma_addr_t	dma;
 	u64		size;
-	u16		q_len;
+	u32		q_len;
 	dma_addr_t	phys_base;
 	void		*base;
 	void		*unalign_base;

From: Dean Nelson <redacted>
Date: 

The Cavium thunder nicvf driver supports rx/tx rings of up to 65536 entries per.
The number of entires are stored in the q_len member of struct q_desc_mem. The
problem is that q_len being a u16, results in 65536 becoming 0.

In getting pointers to descriptors in the rings, the driver uses q_len minus 1
as a mask after incrementing the pointer, in order to go back to the beginning
and not go past the end of the ring.

With the q_len set to 0 the mask is no longer correct and the driver does go
beyond the end of the ring, causing various ills. Usually the first thing that
shows up is a "NETDEV WATCHDOG: enP2p1s0f1 (nicvf): transmit queue 7 timed out"
warning.

This patch remedies the problem by changing q_len to a u32.

Signed-off-by: Dean Nelson <redacted>

Applied, thanks.

Another way to solve this could have been to encode that length
as "length - 1"

On 02/08/2018 02:34 PM, David Miller wrote:

From: Dean Nelson <redacted>
Date:

quoted

The Cavium thunder nicvf driver supports rx/tx rings of up to 65536 entries per.
The number of entires are stored in the q_len member of struct q_desc_mem. The
problem is that q_len being a u16, results in 65536 becoming 0.

In getting pointers to descriptors in the rings, the driver uses q_len minus 1
as a mask after incrementing the pointer, in order to go back to the beginning
and not go past the end of the ring.

With the q_len set to 0 the mask is no longer correct and the driver does go
beyond the end of the ring, causing various ills. Usually the first thing that
shows up is a "NETDEV WATCHDOG: enP2p1s0f1 (nicvf): transmit queue 7 timed out"
warning.

This patch remedies the problem by changing q_len to a u32.

Signed-off-by: Dean Nelson <redacted>

Applied, thanks.

Thank you!

Another way to solve this could have been to encode that length
as "length - 1"

True. I had pondered that, but felt that since changing q_len's type
didn't add any length to the structure and that it was less impactful
from a number-of-lines of code changed perspective, I'd opt for this
route.

Cavium, if you'd prefer this goes the route that Dave just mentioned,
please let me know and I can make a new patch against what's been
applied?

Thanks,
Dean

On Fri, Feb 9, 2018 at 3:27 AM, Dean Nelson [off-list ref] wrote:

On 02/08/2018 02:34 PM, David Miller wrote:

quoted

From: Dean Nelson <redacted>
Date:

quoted

The Cavium thunder nicvf driver supports rx/tx rings of up to 65536
entries per.
The number of entires are stored in the q_len member of struct
q_desc_mem. The
problem is that q_len being a u16, results in 65536 becoming 0.

In getting pointers to descriptors in the rings, the driver uses q_len
minus 1
as a mask after incrementing the pointer, in order to go back to the
beginning
and not go past the end of the ring.

With the q_len set to 0 the mask is no longer correct and the driver does
go
beyond the end of the ring, causing various ills. Usually the first thing
that
shows up is a "NETDEV WATCHDOG: enP2p1s0f1 (nicvf): transmit queue 7
timed out"
warning.

This patch remedies the problem by changing q_len to a u32.

Signed-off-by: Dean Nelson <redacted>

Applied, thanks.

Thank you!

quoted

Another way to solve this could have been to encode that length
as "length - 1"

True. I had pondered that, but felt that since changing q_len's type
didn't add any length to the structure and that it was less impactful
from a number-of-lines of code changed perspective, I'd opt for this
route.

Cavium, if you'd prefer this goes the route that Dave just mentioned,
please let me know and I can make a new patch against what's been
applied?

Thanks for fixing this and i think the current patch is fine.

Thanks,
Sunil.

Thanks,
Dean





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On 02/08/2018 10:29 PM, Sunil Kovvuri wrote:

On Fri, Feb 9, 2018 at 3:27 AM, Dean Nelson [off-list ref] wrote:

quoted

On 02/08/2018 02:34 PM, David Miller wrote:

quoted

From: Dean Nelson <redacted>
Date:

quoted

The Cavium thunder nicvf driver supports rx/tx rings of up to 65536
entries per.

  ...

quoted

quoted

Another way to solve this could have been to encode that length
as "length - 1"

True. I had pondered that, but felt that since changing q_len's type
didn't add any length to the structure and that it was less impactful
from a number-of-lines of code changed perspective, I'd opt for this
route.

Cavium, if you'd prefer this goes the route that Dave just mentioned,
please let me know and I can make a new patch against what's been
applied?

Thanks for fixing this and i think the current patch is fine.

You're welcome. And thanks for responding. So I'll leave things as they
are.