[RFC wpan-next] atusb: add support for trac feature

[RFC wpan-next] atusb: add support for trac feature

[Alexander Aring]

This patch adds support for reading the trac register if atusb firmware
reports tx done. There is currently a feature to compare a sequence
number, if the payload is 1 it tells the driver only the sequence number
is available if it's two there is additional the trac status register as
payload.

Currently the atusb_in_good() function determines if it's a tx done or
rx done if according the payload length. This patch is doing the same
and assumes this behaviour.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
---

Just an RFC, need another weekend to test it.

 drivers/net/ieee802154/atusb.c | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ieee802154/atusb.c b/drivers/net/ieee802154/atusb.c
index 2c338783893d..95a4a3cdc8a4 100644
--- a/drivers/net/ieee802154/atusb.c
+++ b/drivers/net/ieee802154/atusb.c
@@ -191,7 +191,7 @@ static void atusb_work_urbs(struct work_struct *work)
 
 /* ----- Asynchronous USB -------------------------------------------------- */
 
-static void atusb_tx_done(struct atusb *atusb, u8 seq)
+static void atusb_tx_done(struct atusb *atusb, u8 seq, int reason)
 {
 	struct usb_device *usb_dev = atusb->usb_dev;
 	u8 expect = atusb->tx_ack_seq;
@@ -199,7 +199,10 @@ static void atusb_tx_done(struct atusb *atusb, u8 seq)
 	dev_dbg(&usb_dev->dev, "%s (0x%02x/0x%02x)\n", __func__, seq, expect);
 	if (seq == expect) {
 		/* TODO check for ifs handling in firmware */
-		ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
+		if (reason == IEEE802154_SUCCESS)
+			ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
+		else
+			ieee802154_xmit_error(atusb->hw, atusb->tx_skb, reason);
 	} else {
 		/* TODO I experience this case when atusb has a tx complete
 		 * irq before probing, we should fix the firmware it's an
@@ -215,7 +218,8 @@ static void atusb_in_good(struct urb *urb)
 	struct usb_device *usb_dev = urb->dev;
 	struct sk_buff *skb = urb->context;
 	struct atusb *atusb = SKB_ATUSB(skb);
-	u8 len, lqi;
+	int result = IEEE802154_SUCCESS;
+	u8 len, lqi, trac;
 
 	if (!urb->actual_length) {
 		dev_dbg(&usb_dev->dev, "atusb_in: zero-sized URB ?\n");
@@ -224,8 +228,27 @@ static void atusb_in_good(struct urb *urb)
 
 	len = *skb->data;
 
-	if (urb->actual_length == 1) {
-		atusb_tx_done(atusb, len);
+	switch (urb->actual_length) {
+	case 2:
+		trac = TRAC_MASK(*(skb->data + 1));
+		switch (trac) {
+		case TRAC_SUCCESS:
+		case TRAC_SUCCESS_DATA_PENDING:
+			/* already IEEE802154_SUCCESS */
+			break;
+		case TRAC_CHANNEL_ACCESS_FAILURE:
+			result = IEEE802154_CHANNEL_ACCESS_FAILURE;
+			break;
+		case TRAC_NO_ACK:
+			result = IEEE802154_NO_ACK;
+			break;
+		default:
+			result = IEEE802154_SYSTEM_ERROR;
+		}
+
+		fallthrough;
+	case 1:
+		atusb_tx_done(atusb, len, result);
 		return;
 	}
 
-- 
2.31.1

Re: [RFC wpan-next] atusb: add support for trac feature

[Miquel Raynal]

Hi Alexander,

aahringo@redhat.com wrote on Sun,  4 Sep 2022 20:55:44 -0400:

> This patch adds support for reading the trac register if atusb firmware
> reports tx done. There is currently a feature to compare a sequence
> number, if the payload is 1 it tells the driver only the sequence number
> is available if it's two there is additional the trac status register as
> payload.
> 
> Currently the atusb_in_good() function determines if it's a tx done or
> rx done if according the payload length. This patch is doing the same
> and assumes this behaviour.
> 
> Signed-off-by: Alexander Aring <aahringo@redhat.com>
> ---
> 
> Just an RFC, need another weekend to test it.
> 
>  drivers/net/ieee802154/atusb.c | 33 ++++++++++++++++++++++++++++-----
>  1 file changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ieee802154/atusb.c b/drivers/net/ieee802154/atusb.c
> index 2c338783893d..95a4a3cdc8a4 100644
> --- a/drivers/net/ieee802154/atusb.c
> +++ b/drivers/net/ieee802154/atusb.c
> @@ -191,7 +191,7 @@ static void atusb_work_urbs(struct work_struct *work)
>  
>  /* ----- Asynchronous USB -------------------------------------------------- */
>  
> -static void atusb_tx_done(struct atusb *atusb, u8 seq)
> +static void atusb_tx_done(struct atusb *atusb, u8 seq, int reason)
>  {
>  	struct usb_device *usb_dev = atusb->usb_dev;
>  	u8 expect = atusb->tx_ack_seq;
> @@ -199,7 +199,10 @@ static void atusb_tx_done(struct atusb *atusb, u8 seq)
>  	dev_dbg(&usb_dev->dev, "%s (0x%02x/0x%02x)\n", __func__, seq, expect);
>  	if (seq == expect) {
>  		/* TODO check for ifs handling in firmware */
> -		ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> +		if (reason == IEEE802154_SUCCESS)
> +			ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> +		else
> +			ieee802154_xmit_error(atusb->hw, atusb->tx_skb, reason);
>  	} else {
>  		/* TODO I experience this case when atusb has a tx complete
>  		 * irq before probing, we should fix the firmware it's an
> @@ -215,7 +218,8 @@ static void atusb_in_good(struct urb *urb)
>  	struct usb_device *usb_dev = urb->dev;
>  	struct sk_buff *skb = urb->context;
>  	struct atusb *atusb = SKB_ATUSB(skb);
> -	u8 len, lqi;
> +	int result = IEEE802154_SUCCESS;
> +	u8 len, lqi, trac;
>  
>  	if (!urb->actual_length) {
>  		dev_dbg(&usb_dev->dev, "atusb_in: zero-sized URB ?\n");
> @@ -224,8 +228,27 @@ static void atusb_in_good(struct urb *urb)
>  
>  	len = *skb->data;
>  
> -	if (urb->actual_length == 1) {
> -		atusb_tx_done(atusb, len);
> +	switch (urb->actual_length) {
> +	case 2:
> +		trac = TRAC_MASK(*(skb->data + 1));

I've been fighting all night thinking the issues were on the atusb side
(it was horribly difficult to get the atusb toolchain up and running,
I'll send a patch to update the instructions), in particular because of
the data[2] definition which needed to be declared static outside of
the functions (see the other mail) and, I guess, because of this
beginner error: I was using skb->data[1] but of course it can't work.

Anyway, this patch works, I've tested it by:
- associating a device (an Arduino Nano running Zephyr, btw)
- having the atusb disassociating the nano successfully (trac = 0)
- reassociating the nano
- powering off the nano
- trying to disassociate

The disassociation notification transmission fails with a TRAC status
NO_ACK. So:

Tested-by: Miquel Raynal <miquel.raynal@bootlin.com>

I still have the filtering thing to improve, I'm not sure I'll have
time to do that this week. I need some time to prepare the slides now
that the demo works :)

> +		switch (trac) {
> +		case TRAC_SUCCESS:
> +		case TRAC_SUCCESS_DATA_PENDING:
> +			/* already IEEE802154_SUCCESS */
> +			break;
> +		case TRAC_CHANNEL_ACCESS_FAILURE:
> +			result = IEEE802154_CHANNEL_ACCESS_FAILURE;
> +			break;
> +		case TRAC_NO_ACK:
> +			result = IEEE802154_NO_ACK;
> +			break;
> +		default:
> +			result = IEEE802154_SYSTEM_ERROR;
> +		}
> +
> +		fallthrough;
> +	case 1:
> +		atusb_tx_done(atusb, len, result);
>  		return;
>  	}
>  


Thanks,
Miquèl

Re: [RFC wpan-next] atusb: add support for trac feature

[Alexander Aring]

Hi,

On Sun, Sep 4, 2022 at 11:22 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Alexander,
>
> aahringo@redhat.com wrote on Sun,  4 Sep 2022 20:55:44 -0400:
>
> > This patch adds support for reading the trac register if atusb firmware
> > reports tx done. There is currently a feature to compare a sequence
> > number, if the payload is 1 it tells the driver only the sequence number
> > is available if it's two there is additional the trac status register as
> > payload.
> >
> > Currently the atusb_in_good() function determines if it's a tx done or
> > rx done if according the payload length. This patch is doing the same
> > and assumes this behaviour.
> >
> > Signed-off-by: Alexander Aring <aahringo@redhat.com>
> > ---
> >
> > Just an RFC, need another weekend to test it.
> >
> >  drivers/net/ieee802154/atusb.c | 33 ++++++++++++++++++++++++++++-----
> >  1 file changed, 28 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/ieee802154/atusb.c b/drivers/net/ieee802154/atusb.c
> > index 2c338783893d..95a4a3cdc8a4 100644
> > --- a/drivers/net/ieee802154/atusb.c
> > +++ b/drivers/net/ieee802154/atusb.c
> > @@ -191,7 +191,7 @@ static void atusb_work_urbs(struct work_struct *work)
> >
> >  /* ----- Asynchronous USB -------------------------------------------------- */
> >
> > -static void atusb_tx_done(struct atusb *atusb, u8 seq)
> > +static void atusb_tx_done(struct atusb *atusb, u8 seq, int reason)
> >  {
> >       struct usb_device *usb_dev = atusb->usb_dev;
> >       u8 expect = atusb->tx_ack_seq;
> > @@ -199,7 +199,10 @@ static void atusb_tx_done(struct atusb *atusb, u8 seq)
> >       dev_dbg(&usb_dev->dev, "%s (0x%02x/0x%02x)\n", __func__, seq, expect);
> >       if (seq == expect) {
> >               /* TODO check for ifs handling in firmware */
> > -             ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> > +             if (reason == IEEE802154_SUCCESS)
> > +                     ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> > +             else
> > +                     ieee802154_xmit_error(atusb->hw, atusb->tx_skb, reason);
> >       } else {
> >               /* TODO I experience this case when atusb has a tx complete
> >                * irq before probing, we should fix the firmware it's an
> > @@ -215,7 +218,8 @@ static void atusb_in_good(struct urb *urb)
> >       struct usb_device *usb_dev = urb->dev;
> >       struct sk_buff *skb = urb->context;
> >       struct atusb *atusb = SKB_ATUSB(skb);
> > -     u8 len, lqi;
> > +     int result = IEEE802154_SUCCESS;
> > +     u8 len, lqi, trac;
> >
> >       if (!urb->actual_length) {
> >               dev_dbg(&usb_dev->dev, "atusb_in: zero-sized URB ?\n");
> > @@ -224,8 +228,27 @@ static void atusb_in_good(struct urb *urb)
> >
> >       len = *skb->data;
> >
> > -     if (urb->actual_length == 1) {
> > -             atusb_tx_done(atusb, len);
> > +     switch (urb->actual_length) {
> > +     case 2:
> > +             trac = TRAC_MASK(*(skb->data + 1));
>
> I've been fighting all night thinking the issues were on the atusb side
> (it was horribly difficult to get the atusb toolchain up and running,
> I'll send a patch to update the instructions), in particular because of

Really? for me it was just apt install avr-gcc libc-avr (or what the
debian packages name is). Then the dfu-util and be sure you invoke
dfu-util (as root because you might need some udev rules otherwise)
when the atusb is booting up.

> the data[2] definition which needed to be declared static outside of
> the functions (see the other mail) and, I guess, because of this
> beginner error: I was using skb->data[1] but of course it can't work.
>

mhh, I am sorry. I am not sure if I understand what you mean? Does the
firmware patch have issues regarding data[2]?

> Anyway, this patch works, I've tested it by:
> - associating a device (an Arduino Nano running Zephyr, btw)
> - having the atusb disassociating the nano successfully (trac = 0)
> - reassociating the nano
> - powering off the nano
> - trying to disassociate
>
> The disassociation notification transmission fails with a TRAC status
> NO_ACK. So:
>
> Tested-by: Miquel Raynal <miquel.raynal@bootlin.com>
>
> I still have the filtering thing to improve, I'm not sure I'll have
> time to do that this week. I need some time to prepare the slides now
> that the demo works :)
>

ok, no problem. Thanks for testing it. I am happy that if I could help
you here a little bit.

- Alex

Re: [RFC wpan-next] atusb: add support for trac feature

[Miquel Raynal]

Hi Alexander,

aahringo@redhat.com wrote on Mon, 5 Sep 2022 07:16:42 -0400:

> Hi,
> 
> On Sun, Sep 4, 2022 at 11:22 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> >
> > Hi Alexander,
> >
> > aahringo@redhat.com wrote on Sun,  4 Sep 2022 20:55:44 -0400:
> >  
> > > This patch adds support for reading the trac register if atusb firmware
> > > reports tx done. There is currently a feature to compare a sequence
> > > number, if the payload is 1 it tells the driver only the sequence number
> > > is available if it's two there is additional the trac status register as
> > > payload.
> > >
> > > Currently the atusb_in_good() function determines if it's a tx done or
> > > rx done if according the payload length. This patch is doing the same
> > > and assumes this behaviour.
> > >
> > > Signed-off-by: Alexander Aring <aahringo@redhat.com>
> > > ---
> > >
> > > Just an RFC, need another weekend to test it.
> > >
> > >  drivers/net/ieee802154/atusb.c | 33 ++++++++++++++++++++++++++++-----
> > >  1 file changed, 28 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/net/ieee802154/atusb.c b/drivers/net/ieee802154/atusb.c
> > > index 2c338783893d..95a4a3cdc8a4 100644
> > > --- a/drivers/net/ieee802154/atusb.c
> > > +++ b/drivers/net/ieee802154/atusb.c
> > > @@ -191,7 +191,7 @@ static void atusb_work_urbs(struct work_struct *work)
> > >
> > >  /* ----- Asynchronous USB -------------------------------------------------- */
> > >
> > > -static void atusb_tx_done(struct atusb *atusb, u8 seq)
> > > +static void atusb_tx_done(struct atusb *atusb, u8 seq, int reason)
> > >  {
> > >       struct usb_device *usb_dev = atusb->usb_dev;
> > >       u8 expect = atusb->tx_ack_seq;
> > > @@ -199,7 +199,10 @@ static void atusb_tx_done(struct atusb *atusb, u8 seq)
> > >       dev_dbg(&usb_dev->dev, "%s (0x%02x/0x%02x)\n", __func__, seq, expect);
> > >       if (seq == expect) {
> > >               /* TODO check for ifs handling in firmware */
> > > -             ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> > > +             if (reason == IEEE802154_SUCCESS)
> > > +                     ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> > > +             else
> > > +                     ieee802154_xmit_error(atusb->hw, atusb->tx_skb, reason);
> > >       } else {
> > >               /* TODO I experience this case when atusb has a tx complete
> > >                * irq before probing, we should fix the firmware it's an
> > > @@ -215,7 +218,8 @@ static void atusb_in_good(struct urb *urb)
> > >       struct usb_device *usb_dev = urb->dev;
> > >       struct sk_buff *skb = urb->context;
> > >       struct atusb *atusb = SKB_ATUSB(skb);
> > > -     u8 len, lqi;
> > > +     int result = IEEE802154_SUCCESS;
> > > +     u8 len, lqi, trac;
> > >
> > >       if (!urb->actual_length) {
> > >               dev_dbg(&usb_dev->dev, "atusb_in: zero-sized URB ?\n");
> > > @@ -224,8 +228,27 @@ static void atusb_in_good(struct urb *urb)
> > >
> > >       len = *skb->data;
> > >
> > > -     if (urb->actual_length == 1) {
> > > -             atusb_tx_done(atusb, len);
> > > +     switch (urb->actual_length) {
> > > +     case 2:
> > > +             trac = TRAC_MASK(*(skb->data + 1));  
> >
> > I've been fighting all night thinking the issues were on the atusb side
> > (it was horribly difficult to get the atusb toolchain up and running,
> > I'll send a patch to update the instructions), in particular because of  
> 
> Really? for me it was just apt install avr-gcc libc-avr (or what the
> debian packages name is).

I feel so bad. All the instructions I could find (from 2011) advised to
download an old gcc, an old binutils and old avr-lib, to compile
everything by hand... 2 out of 3 archives returned a 404 error, the
builds were chaotic I had to disable -Werror and fix many issues
manually, then I had to fight with binutils assembler failing, I tried
4 different versions before I got it right... I did write a commit to
update the instructions but if you say that just downloading the stock
pre-compiled binaries worked I am a bit disappointed because the
instructions specifically told not to do so.

> Then the dfu-util and be sure you invoke
> dfu-util (as root because you might need some udev rules otherwise)
> when the atusb is booting up.

Yes, dfu worked right away, very nice tool.

> > the data[2] definition which needed to be declared static outside of
> > the functions (see the other mail) and, I guess, because of this
> > beginner error: I was using skb->data[1] but of course it can't work.
> >  
> 
> mhh, I am sorry. I am not sure if I understand what you mean? Does the
> firmware patch have issues regarding data[2]?

Actually I'm wrong.
You did: *(skb->data + 1), which works.
I did: skb->data[1], which does not.
I thought that my mistake was related to data being a void *, but it's
a char * so both should work. I don't know why it failed, maybe my
attention level was too low and I missed something else.

> > Anyway, this patch works, I've tested it by:
> > - associating a device (an Arduino Nano running Zephyr, btw)
> > - having the atusb disassociating the nano successfully (trac = 0)
> > - reassociating the nano
> > - powering off the nano
> > - trying to disassociate
> >
> > The disassociation notification transmission fails with a TRAC status
> > NO_ACK. So:
> >
> > Tested-by: Miquel Raynal <miquel.raynal@bootlin.com>
> >
> > I still have the filtering thing to improve, I'm not sure I'll have
> > time to do that this week. I need some time to prepare the slides now
> > that the demo works :)
> >  
> 
> ok, no problem. Thanks for testing it. I am happy that if I could help
> you here a little bit.
> 
> - Alex
> 


Thanks,
Miquèl

Re: [RFC wpan-next] atusb: add support for trac feature

[Alexander Aring]

Hi,

On Mon, Sep 5, 2022 at 10:19 AM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
>
> Hi Alexander,
>
> aahringo@redhat.com wrote on Mon, 5 Sep 2022 07:16:42 -0400:
>
> > Hi,
> >
> > On Sun, Sep 4, 2022 at 11:22 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
> > >
> > > Hi Alexander,
> > >
> > > aahringo@redhat.com wrote on Sun,  4 Sep 2022 20:55:44 -0400:
> > >
> > > > This patch adds support for reading the trac register if atusb firmware
> > > > reports tx done. There is currently a feature to compare a sequence
> > > > number, if the payload is 1 it tells the driver only the sequence number
> > > > is available if it's two there is additional the trac status register as
> > > > payload.
> > > >
> > > > Currently the atusb_in_good() function determines if it's a tx done or
> > > > rx done if according the payload length. This patch is doing the same
> > > > and assumes this behaviour.
> > > >
> > > > Signed-off-by: Alexander Aring <aahringo@redhat.com>
> > > > ---
> > > >
> > > > Just an RFC, need another weekend to test it.
> > > >
> > > >  drivers/net/ieee802154/atusb.c | 33 ++++++++++++++++++++++++++++-----
> > > >  1 file changed, 28 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/drivers/net/ieee802154/atusb.c b/drivers/net/ieee802154/atusb.c
> > > > index 2c338783893d..95a4a3cdc8a4 100644
> > > > --- a/drivers/net/ieee802154/atusb.c
> > > > +++ b/drivers/net/ieee802154/atusb.c
> > > > @@ -191,7 +191,7 @@ static void atusb_work_urbs(struct work_struct *work)
> > > >
> > > >  /* ----- Asynchronous USB -------------------------------------------------- */
> > > >
> > > > -static void atusb_tx_done(struct atusb *atusb, u8 seq)
> > > > +static void atusb_tx_done(struct atusb *atusb, u8 seq, int reason)
> > > >  {
> > > >       struct usb_device *usb_dev = atusb->usb_dev;
> > > >       u8 expect = atusb->tx_ack_seq;
> > > > @@ -199,7 +199,10 @@ static void atusb_tx_done(struct atusb *atusb, u8 seq)
> > > >       dev_dbg(&usb_dev->dev, "%s (0x%02x/0x%02x)\n", __func__, seq, expect);
> > > >       if (seq == expect) {
> > > >               /* TODO check for ifs handling in firmware */
> > > > -             ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> > > > +             if (reason == IEEE802154_SUCCESS)
> > > > +                     ieee802154_xmit_complete(atusb->hw, atusb->tx_skb, false);
> > > > +             else
> > > > +                     ieee802154_xmit_error(atusb->hw, atusb->tx_skb, reason);
> > > >       } else {
> > > >               /* TODO I experience this case when atusb has a tx complete
> > > >                * irq before probing, we should fix the firmware it's an
> > > > @@ -215,7 +218,8 @@ static void atusb_in_good(struct urb *urb)
> > > >       struct usb_device *usb_dev = urb->dev;
> > > >       struct sk_buff *skb = urb->context;
> > > >       struct atusb *atusb = SKB_ATUSB(skb);
> > > > -     u8 len, lqi;
> > > > +     int result = IEEE802154_SUCCESS;
> > > > +     u8 len, lqi, trac;
> > > >
> > > >       if (!urb->actual_length) {
> > > >               dev_dbg(&usb_dev->dev, "atusb_in: zero-sized URB ?\n");
> > > > @@ -224,8 +228,27 @@ static void atusb_in_good(struct urb *urb)
> > > >
> > > >       len = *skb->data;
> > > >
> > > > -     if (urb->actual_length == 1) {
> > > > -             atusb_tx_done(atusb, len);
> > > > +     switch (urb->actual_length) {
> > > > +     case 2:
> > > > +             trac = TRAC_MASK(*(skb->data + 1));
> > >
> > > I've been fighting all night thinking the issues were on the atusb side
> > > (it was horribly difficult to get the atusb toolchain up and running,
> > > I'll send a patch to update the instructions), in particular because of
> >
> > Really? for me it was just apt install avr-gcc libc-avr (or what the
> > debian packages name is).
>
> I feel so bad. All the instructions I could find (from 2011) advised to
> download an old gcc, an old binutils and old avr-lib, to compile
> everything by hand... 2 out of 3 archives returned a 404 error, the
> builds were chaotic I had to disable -Werror and fix many issues
> manually, then I had to fight with binutils assembler failing, I tried
> 4 different versions before I got it right... I did write a commit to
> update the instructions but if you say that just downloading the stock
> pre-compiled binaries worked I am a bit disappointed because the
> instructions specifically told not to do so.
>

I am sorry that you had those problems.

> > Then the dfu-util and be sure you invoke
> > dfu-util (as root because you might need some udev rules otherwise)
> > when the atusb is booting up.
>
> Yes, dfu worked right away, very nice tool.
>
> > > the data[2] definition which needed to be declared static outside of
> > > the functions (see the other mail) and, I guess, because of this
> > > beginner error: I was using skb->data[1] but of course it can't work.
> > >
> >
> > mhh, I am sorry. I am not sure if I understand what you mean? Does the
> > firmware patch have issues regarding data[2]?
>
> Actually I'm wrong.
> You did: *(skb->data + 1), which works.
> I did: skb->data[1], which does not.
> I thought that my mistake was related to data being a void *, but it's
> a char * so both should work. I don't know why it failed, maybe my
> attention level was too low and I missed something else.

I don't see a difference. No idea...

- Alex