[PATCH RFC 0/2] huawei_cdc_ncm: new NCM TX stack for Huawei-style NCM

[PATCH RFC 0/2] huawei_cdc_ncm: new NCM TX stack for Huawei-style NCM

[Enrico Mioso]

This is an ALFA version of my new NCM TX engine, built with huawei-style NCM and flexibility in mind.
The main goal is to allow foreasily re-ordering NCM frame content.
Basic communication works - but an usbnet EVENT_RX_MEMORY will stop the process after some packets.
Any idea or comment about any aspect of this code is really apreciated - 
including suggestions for style and over-long lines problematic to break down, 
at least for me.


Lots of lines longer than 80 chars seemed not easily breakable to me: any 
suggestion is welcome.

Enrico Mioso (2):
  cdc_ncm: export cdc_ncm_align_tail
  huawei_cdc_ncm: introduce new TX ncm stack

 drivers/net/usb/cdc_ncm.c        |   3 +-
 drivers/net/usb/huawei_cdc_ncm.c | 187 ++++++++++++++++++++++++++++++++++++++-
 include/linux/usb/cdc_ncm.h      |   1 +
 3 files changed, 188 insertions(+), 3 deletions(-)

-- 
2.4.4

[PATCH RFC] 1/2 cdc_ncm: export cdc_ncm_align_tail

[Enrico Mioso]

Export this function to allow for reusing it in other drivers needing NCM
frames alignment, such as the huawei_cdc_ncm one.

Signed-off-by: Enrico Mioso <mrkiko.rs@gmail.com>
---
 drivers/net/usb/cdc_ncm.c   | 3 ++-
 include/linux/usb/cdc_ncm.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index 8067b8f..1a8b619 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -967,7 +967,7 @@ static int cdc_ncm_bind(struct usbnet *dev, struct usb_interface *intf)
 	return ret;
 }
 
-static void cdc_ncm_align_tail(struct sk_buff *skb, size_t modulus, size_t remainder, size_t max)
+void cdc_ncm_align_tail(struct sk_buff *skb, size_t modulus, size_t remainder, size_t max)
 {
 	size_t align = ALIGN(skb->len, modulus) - skb->len + remainder;
 
@@ -976,6 +976,7 @@ static void cdc_ncm_align_tail(struct sk_buff *skb, size_t modulus, size_t remai
 	if (align && skb_tailroom(skb) >= align)
 		memset(skb_put(skb, align), 0, align);
 }
+EXPORT_SYMBOL_GPL(cdc_ncm_align_tail);
 
 /* return a pointer to a valid struct usb_cdc_ncm_ndp16 of type sign, possibly
  * allocating a new one within skb
diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
index 7c9b484..8fe7ef0 100644
--- a/include/linux/usb/cdc_ncm.h
+++ b/include/linux/usb/cdc_ncm.h
@@ -141,5 +141,6 @@ int cdc_ncm_rx_verify_ndp16(struct sk_buff *skb_in, int ndpoffset);
 struct sk_buff *
 cdc_ncm_tx_fixup(struct usbnet *dev, struct sk_buff *skb, gfp_t flags);
 int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in);
+void cdc_ncm_align_tail(struct sk_buff *skb, size_t modulus, size_t remainder, size_t max);
 
 #endif /* __LINUX_USB_CDC_NCM_H */
-- 
2.4.4

[PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Enrico Mioso]

This patch introduces a new NCM tx engine, able to operate in standard-
and huawei-style mode.
In the first case, the NDP is disposed after the initial headers and
before any datagram.

What works:
- is able to communicate with compliant NCM devices:
	I tested this with a board running the Linux g_ncm gadget driver.

What doesn't work:
- After some packets I start gettint LOTS of EVENT_RX_MEMORY from usbnet,
	which fails to allocate an RX SKB in rx_submit(). Don't understand why,
	any suggestion would be very welcome.

The tx_fixup function given here, even if actually working, should be
considered as an example: the NCM manager is used here simulating the
cdc_ncm.c behaviour.

Signed-off-by: Enrico Mioso <mrkiko.rs@gmail.com>
---
 drivers/net/usb/huawei_cdc_ncm.c | 187 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 185 insertions(+), 2 deletions(-)

diff --git a/drivers/net/usb/huawei_cdc_ncm.c b/drivers/net/usb/huawei_cdc_ncm.c
index 735f7da..217802a 100644
--- a/drivers/net/usb/huawei_cdc_ncm.c
+++ b/drivers/net/usb/huawei_cdc_ncm.c
@@ -29,6 +29,35 @@
 #include <linux/usb/cdc-wdm.h>
 #include <linux/usb/cdc_ncm.h>
 
+/* NCM management operations: */
+
+/* NCM_INIT_FRAME: prepare for a new frame.
+ * NTH16 header is written to output SKB, NDP data is reset and last
+ * committed NDP pointer set to NULL.
+ * Now, data may be added to this NCM package.
+ */
+#define NCM_INIT_FRAME		1
+
+/* NCM_UPDATE_NDP: adds data to an NDP structure, hence updating it.
+ * Some checks are performed to be sure data fits in, respecting device and
+ * spec constrains.
+ * Normally the NDP is kept in memory and committed to the SKB only when
+ * requested. However, calling this "method" after NCM_COMMIT_NDP, causes it to
+ * work directly on the already committed SKB copy. this allows for flexibility
+ * in frame ordering.
+ */
+#define NCM_UPDATE_NDP		2
+
+/* Write NDP: commits NDP to output SKB.
+ * This method should be called only once per frame.
+ */
+#define NCM_COMMIT_NDP		3
+
+/* Finalizes NTH16 header: to be called when working in
+ * update-already-committed mode.
+ */
+#define NCM_FINALIZE_NTH	5
+
 /* Driver data */
 struct huawei_cdc_ncm_state {
 	struct cdc_ncm_ctx *ctx;
@@ -36,6 +65,16 @@ struct huawei_cdc_ncm_state {
 	struct usb_driver *subdriver;
 	struct usb_interface *control;
 	struct usb_interface *data;
+
+	/* Keeps track of where data starts and ends in SKBs. */
+	int data_start;
+	int data_len;
+
+	/* Last committed NDP for post-commit operations. */
+	struct usb_cdc_ncm_ndp16 *skb_ndp;
+
+	/* Non-committed NDP */
+	struct usb_cdc_ncm_ndp16 *ndp;
 };
 
 static int huawei_cdc_ncm_manage_power(struct usbnet *usbnet_dev, int on)
@@ -53,6 +92,149 @@ static int huawei_cdc_ncm_manage_power(struct usbnet *usbnet_dev, int on)
 	return 0;
 }
 
+/* huawei_ncm_mgmt: flexible TX NCM manager.
+ *
+ * Once a non-zero status value is rturned, current frame should be discarded
+ * and operations restarted from scratch.
+ */
+int
+huawei_ncm_mgmt(struct usbnet *dev,
+		struct huawei_cdc_ncm_state *drvstate, struct sk_buff *skb_out, int mode) {
+	struct usb_cdc_ncm_nth16 *nth16 = (struct usb_cdc_ncm_nth16 *)skb_out->data;
+	struct cdc_ncm_ctx *ctx = drvstate->ctx;
+	struct usb_cdc_ncm_ndp16 *ndp16 = NULL;
+	int ret = -EINVAL;
+	u16 ndplen, index;
+
+	switch (mode) {
+	case NCM_INIT_FRAME:
+
+		/* Write a new NTH16 header */
+		nth16 = (struct usb_cdc_ncm_nth16 *)memset(skb_put(skb_out, sizeof(struct usb_cdc_ncm_nth16)), 0, sizeof(struct usb_cdc_ncm_nth16));
+		if (!nth16) {
+			ret = -EINVAL;
+			goto error;
+		}
+
+		/* NTH16 signature and header length are known a-priori. */
+		nth16->dwSignature = cpu_to_le32(USB_CDC_NCM_NTH16_SIGN);
+		nth16->wHeaderLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
+
+		/* TX sequence numbering */
+		nth16->wSequence = cpu_to_le16(ctx->tx_seq++);
+
+		/* Forget about previous SKB NDP */
+		drvstate->skb_ndp = NULL;
+
+		/* Allocate a new NDP */
+		ndp16 = kzalloc(ctx->max_ndp_size, GFP_NOIO);
+		if (!ndp16)
+			return ret;
+
+		/* Prepare a new NDP to add data on subsequent calls. */
+		drvstate->ndp = memset(ndp16, 0, ctx->max_ndp_size);
+
+		/* Initial NDP length */
+		ndp16->wLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_ndp16) + sizeof(struct usb_cdc_ncm_dpe16));
+
+		/* Frame signature: to be reworked in general. */
+			ndp16->dwSignature = cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN);
+
+			ret = 0;
+			break;
+
+	case NCM_UPDATE_NDP:
+
+		if (drvstate->skb_ndp) {
+			ndp16 = drvstate->skb_ndp;
+		} else {
+			ndp16 = drvstate->ndp;
+
+			/* Do we have enough space for the data? */
+			if (skb_out->len + ctx->max_ndp_size > ctx->tx_max)
+				goto error;
+		}
+
+		/* Calculate frame number within this NDP */
+		ndplen = le16_to_cpu(ndp16->wLength);
+		index = (ndplen - sizeof(struct usb_cdc_ncm_ndp16)) / sizeof(struct usb_cdc_ncm_dpe16) - 1;
+
+		if (index >= CDC_NCM_DPT_DATAGRAMS_MAX)
+			goto error;
+
+		/* tx_max shouldn't be exceeded after committing. */
+		if (ndplen + sizeof(struct usb_cdc_ncm_dpe16) > ctx->tx_max)
+				goto error;
+
+		/* Adding a DPT entry. */
+		ndp16->dpe16[index].wDatagramLength = cpu_to_le16(drvstate->data_len);
+		ndp16->dpe16[index].wDatagramIndex = cpu_to_le16(drvstate->data_start);
+		ndp16->wLength = cpu_to_le16(ndplen + sizeof(struct usb_cdc_ncm_dpe16));
+
+		ret = 0;
+		break;
+
+	case NCM_COMMIT_NDP:
+
+		if (drvstate->skb_ndp)
+			goto error;	/* Call this only once please. */
+
+		ndp16 = drvstate->ndp;
+
+		nth16->wNdpIndex = cpu_to_le16(skb_out->len);
+
+		/* "commit" NDP */
+		drvstate->skb_ndp = memcpy(skb_put(skb_out, ctx->max_ndp_size), ndp16, ctx->max_ndp_size);
+
+		kfree(ndp16);
+		ndp16 = NULL;
+		drvstate->ndp = NULL;
+
+	case NCM_FINALIZE_NTH:
+
+		/* Finalize NTH16 header, setting it's block length */
+		nth16->wBlockLength = cpu_to_le16(skb_out->len);
+
+		ret = 0;
+		break;
+	default:
+		break;
+	}
+
+error:
+	if (ret)
+		kfree(drvstate->ndp);
+	return ret;
+}
+
+/* XXX rewrite, not multipacket */
+struct sk_buff *
+huawei_ncm_tx_fixup(struct usbnet *dev, struct sk_buff *skb_in, gfp_t flags) {
+	struct huawei_cdc_ncm_state *drvstate = (void *)&dev->data;
+	struct cdc_ncm_ctx *ctx = drvstate->ctx;
+	struct sk_buff *skb_out;
+	int status;
+
+	skb_out = alloc_skb(ctx->tx_max, GFP_ATOMIC);
+
+	status = huawei_ncm_mgmt(dev, drvstate, skb_out, NCM_INIT_FRAME);
+
+	cdc_ncm_align_tail(skb_out, ctx->tx_ndp_modulus, 0, ctx->tx_max);
+	status = huawei_ncm_mgmt(dev, drvstate, skb_out, NCM_COMMIT_NDP);
+
+	cdc_ncm_align_tail(skb_out,  ctx->tx_modulus, ctx->tx_remainder, ctx->tx_max);
+	drvstate->data_start = skb_out->len;
+	memcpy(skb_put(skb_out, skb_in->len), skb_in->data, skb_in->len);
+	drvstate->data_len = skb_out->len - drvstate->data_start;
+
+	status = huawei_ncm_mgmt(dev, drvstate, skb_out, NCM_UPDATE_NDP);
+
+	status = huawei_ncm_mgmt(dev, drvstate, skb_out, NCM_FINALIZE_NTH);
+
+	kfree_skb(skb_in);
+	return skb_out;
+}
+
 static int huawei_cdc_ncm_wdm_manage_power(struct usb_interface *intf,
 					   int status)
 {
@@ -175,12 +357,13 @@ err:
 
 static const struct driver_info huawei_cdc_ncm_info = {
 	.description = "Huawei CDC NCM device",
-	.flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN,
+	/* .flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN, */
+	.flags = FLAG_NO_SETINT | FLAG_WWAN,
 	.bind = huawei_cdc_ncm_bind,
 	.unbind = huawei_cdc_ncm_unbind,
 	.manage_power = huawei_cdc_ncm_manage_power,
 	.rx_fixup = cdc_ncm_rx_fixup,
-	.tx_fixup = cdc_ncm_tx_fixup,
+	.tx_fixup = huawei_ncm_tx_fixup,
 };
 
 static const struct usb_device_id huawei_cdc_ncm_devs[] = {
-- 
2.4.4

Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Oliver Neukum]

On Tue, 2015-06-23 at 00:32 +0200, Enrico Mioso wrote:
> This patch introduces a new NCM tx engine, able to operate in standard-
> and huawei-style mode.
> In the first case, the NDP is disposed after the initial headers and
> before any datagram.
> 
> What works:
> - is able to communicate with compliant NCM devices:
> 	I tested this with a board running the Linux g_ncm gadget driver.
> 
> What doesn't work:
> - After some packets I start gettint LOTS of EVENT_RX_MEMORY from usbnet,
> 	which fails to allocate an RX SKB in rx_submit(). Don't understand why,
> 	any suggestion would be very welcome.
> 
> The tx_fixup function given here, even if actually working, should be
> considered as an example: the NCM manager is used here simulating the
> cdc_ncm.c behaviour.
> 
> Signed-off-by: Enrico Mioso <mrkiko.rs-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> ---
>  drivers/net/usb/huawei_cdc_ncm.c | 187 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 185 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/usb/huawei_cdc_ncm.c b/drivers/net/usb/huawei_cdc_ncm.c
> index 735f7da..217802a 100644
> --- a/drivers/net/usb/huawei_cdc_ncm.c
> +++ b/drivers/net/usb/huawei_cdc_ncm.c
> @@ -29,6 +29,35 @@
>  #include <linux/usb/cdc-wdm.h>
>  #include <linux/usb/cdc_ncm.h>
>  
> +/* NCM management operations: */
> +
> +/* NCM_INIT_FRAME: prepare for a new frame.
> + * NTH16 header is written to output SKB, NDP data is reset and last
> + * committed NDP pointer set to NULL.
> + * Now, data may be added to this NCM package.
> + */
> +#define NCM_INIT_FRAME		1
> +
> +/* NCM_UPDATE_NDP: adds data to an NDP structure, hence updating it.
> + * Some checks are performed to be sure data fits in, respecting device and
> + * spec constrains.
> + * Normally the NDP is kept in memory and committed to the SKB only when
> + * requested. However, calling this "method" after NCM_COMMIT_NDP, causes it to
> + * work directly on the already committed SKB copy. this allows for flexibility
> + * in frame ordering.
> + */
> +#define NCM_UPDATE_NDP		2
> +
> +/* Write NDP: commits NDP to output SKB.
> + * This method should be called only once per frame.
> + */
> +#define NCM_COMMIT_NDP		3
> +
> +/* Finalizes NTH16 header: to be called when working in
> + * update-already-committed mode.
> + */
> +#define NCM_FINALIZE_NTH	5
> +
>  /* Driver data */
>  struct huawei_cdc_ncm_state {
>  	struct cdc_ncm_ctx *ctx;
> @@ -36,6 +65,16 @@ struct huawei_cdc_ncm_state {
>  	struct usb_driver *subdriver;
>  	struct usb_interface *control;
>  	struct usb_interface *data;
> +
> +	/* Keeps track of where data starts and ends in SKBs. */
> +	int data_start;
> +	int data_len;
> +
> +	/* Last committed NDP for post-commit operations. */
> +	struct usb_cdc_ncm_ndp16 *skb_ndp;
> +
> +	/* Non-committed NDP */
> +	struct usb_cdc_ncm_ndp16 *ndp;
>  };
>  
>  static int huawei_cdc_ncm_manage_power(struct usbnet *usbnet_dev, int on)
> @@ -53,6 +92,149 @@ static int huawei_cdc_ncm_manage_power(struct usbnet *usbnet_dev, int on)
>  	return 0;
>  }
>  
> +/* huawei_ncm_mgmt: flexible TX NCM manager.
> + *
> + * Once a non-zero status value is rturned, current frame should be discarded
> + * and operations restarted from scratch.
> + */

Is there any advantage in keeping this in a single function?

> +int
> +huawei_ncm_mgmt(struct usbnet *dev,
> +		struct huawei_cdc_ncm_state *drvstate, struct sk_buff *skb_out, int mode) {
> +	struct usb_cdc_ncm_nth16 *nth16 = (struct usb_cdc_ncm_nth16 *)skb_out->data;
> +	struct cdc_ncm_ctx *ctx = drvstate->ctx;
> +	struct usb_cdc_ncm_ndp16 *ndp16 = NULL;
> +	int ret = -EINVAL;
> +	u16 ndplen, index;
> +
> +	switch (mode) {
> +	case NCM_INIT_FRAME:
> +
> +		/* Write a new NTH16 header */
> +		nth16 = (struct usb_cdc_ncm_nth16 *)memset(skb_put(skb_out, sizeof(struct usb_cdc_ncm_nth16)), 0, sizeof(struct usb_cdc_ncm_nth16));
> +		if (!nth16) {
> +			ret = -EINVAL;
> +			goto error;
> +		}
> +
> +		/* NTH16 signature and header length are known a-priori. */
> +		nth16->dwSignature = cpu_to_le32(USB_CDC_NCM_NTH16_SIGN);
> +		nth16->wHeaderLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
> +
> +		/* TX sequence numbering */
> +		nth16->wSequence = cpu_to_le16(ctx->tx_seq++);
> +
> +		/* Forget about previous SKB NDP */
> +		drvstate->skb_ndp = NULL;

This is probably better done after you know you cannot fail.

> +
> +		/* Allocate a new NDP */
> +		ndp16 = kzalloc(ctx->max_ndp_size, GFP_NOIO);

Where is this freed?

> +		if (!ndp16)
> +			return ret;
> +
> +		/* Prepare a new NDP to add data on subsequent calls. */
> +		drvstate->ndp = memset(ndp16, 0, ctx->max_ndp_size);

Either kzalloc() or memset(). Using both never makes sense.

> +
> +		/* Initial NDP length */
> +		ndp16->wLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_ndp16) + sizeof(struct usb_cdc_ncm_dpe16));
> +
> +		/* Frame signature: to be reworked in general. */
> +			ndp16->dwSignature = cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN);
> +
> +			ret = 0;
> +			break;
> +
> +	case NCM_UPDATE_NDP:
> +
> +		if (drvstate->skb_ndp) {
> +			ndp16 = drvstate->skb_ndp;
> +		} else {
> +			ndp16 = drvstate->ndp;
> +
> +			/* Do we have enough space for the data? */
> +			if (skb_out->len + ctx->max_ndp_size > ctx->tx_max)
> +				goto error;
> +		}
> +
> +		/* Calculate frame number within this NDP */
> +		ndplen = le16_to_cpu(ndp16->wLength);
> +		index = (ndplen - sizeof(struct usb_cdc_ncm_ndp16)) / sizeof(struct usb_cdc_ncm_dpe16) - 1;
> +
> +		if (index >= CDC_NCM_DPT_DATAGRAMS_MAX)
> +			goto error;
> +
> +		/* tx_max shouldn't be exceeded after committing. */
> +		if (ndplen + sizeof(struct usb_cdc_ncm_dpe16) > ctx->tx_max)
> +				goto error;
> +
> +		/* Adding a DPT entry. */
> +		ndp16->dpe16[index].wDatagramLength = cpu_to_le16(drvstate->data_len);
> +		ndp16->dpe16[index].wDatagramIndex = cpu_to_le16(drvstate->data_start);
> +		ndp16->wLength = cpu_to_le16(ndplen + sizeof(struct usb_cdc_ncm_dpe16));
> +
> +		ret = 0;
> +		break;
> +
> +	case NCM_COMMIT_NDP:
> +
> +		if (drvstate->skb_ndp)
> +			goto error;	/* Call this only once please. */
> +
> +		ndp16 = drvstate->ndp;
> +
> +		nth16->wNdpIndex = cpu_to_le16(skb_out->len);
> +
> +		/* "commit" NDP */
> +		drvstate->skb_ndp = memcpy(skb_put(skb_out, ctx->max_ndp_size), ndp16, ctx->max_ndp_size);
> +
> +		kfree(ndp16);
> +		ndp16 = NULL;
> +		drvstate->ndp = NULL;
> +
> +	case NCM_FINALIZE_NTH:
> +
> +		/* Finalize NTH16 header, setting it's block length */
> +		nth16->wBlockLength = cpu_to_le16(skb_out->len);
> +
> +		ret = 0;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +error:

The purpose of a label is kind of defeated by having a conditional after
it.

> +	if (ret)
> +		kfree(drvstate->ndp);
> +	return ret;
> +}

	Regards
		Oliver


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Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Enrico Mioso]

Hi Oliver.
Thank you for your patience, and review. I apreciated it very much.

On Thu, 25 Jun 2015, Oliver Neukum wrote:

> Date: Thu, 25 Jun 2015 11:49:29
> From: Oliver Neukum <oneukum@suse.com>
> To: Enrico Mioso <mrkiko.rs@gmail.com>
> Cc: linux-usb@vger.kernel.org, netdev@vger.kernel.org
> Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
> 
> On Tue, 2015-06-23 at 00:32 +0200, Enrico Mioso wrote:
>> This patch introduces a new NCM tx engine, able to operate in standard-
>> and huawei-style mode.
>> In the first case, the NDP is disposed after the initial headers and
>> before any datagram.
>>
>> What works:
>> - is able to communicate with compliant NCM devices:
>> 	I tested this with a board running the Linux g_ncm gadget driver.
>>
>> What doesn't work:
>> - After some packets I start gettint LOTS of EVENT_RX_MEMORY from usbnet,
>> 	which fails to allocate an RX SKB in rx_submit(). Don't understand why,
>> 	any suggestion would be very welcome.
>>
>> The tx_fixup function given here, even if actually working, should be
>> considered as an example: the NCM manager is used here simulating the
>> cdc_ncm.c behaviour.
>>
>> Signed-off-by: Enrico Mioso <mrkiko.rs@gmail.com>
>> ---
>>  drivers/net/usb/huawei_cdc_ncm.c | 187 ++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 185 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/usb/huawei_cdc_ncm.c b/drivers/net/usb/huawei_cdc_ncm.c
>> index 735f7da..217802a 100644
>> --- a/drivers/net/usb/huawei_cdc_ncm.c
>> +++ b/drivers/net/usb/huawei_cdc_ncm.c
>> @@ -29,6 +29,35 @@
>>  #include <linux/usb/cdc-wdm.h>
>>  #include <linux/usb/cdc_ncm.h>
>>
>> +/* NCM management operations: */
>> +
>> +/* NCM_INIT_FRAME: prepare for a new frame.
>> + * NTH16 header is written to output SKB, NDP data is reset and last
>> + * committed NDP pointer set to NULL.
>> + * Now, data may be added to this NCM package.
>> + */
>> +#define NCM_INIT_FRAME		1
>> +
>> +/* NCM_UPDATE_NDP: adds data to an NDP structure, hence updating it.
>> + * Some checks are performed to be sure data fits in, respecting device and
>> + * spec constrains.
>> + * Normally the NDP is kept in memory and committed to the SKB only when
>> + * requested. However, calling this "method" after NCM_COMMIT_NDP, causes it to
>> + * work directly on the already committed SKB copy. this allows for flexibility
>> + * in frame ordering.
>> + */
>> +#define NCM_UPDATE_NDP		2
>> +
>> +/* Write NDP: commits NDP to output SKB.
>> + * This method should be called only once per frame.
>> + */
>> +#define NCM_COMMIT_NDP		3
>> +
>> +/* Finalizes NTH16 header: to be called when working in
>> + * update-already-committed mode.
>> + */
>> +#define NCM_FINALIZE_NTH	5
>> +
>>  /* Driver data */
>>  struct huawei_cdc_ncm_state {
>>  	struct cdc_ncm_ctx *ctx;
>> @@ -36,6 +65,16 @@ struct huawei_cdc_ncm_state {
>>  	struct usb_driver *subdriver;
>>  	struct usb_interface *control;
>>  	struct usb_interface *data;
>> +
>> +	/* Keeps track of where data starts and ends in SKBs. */
>> +	int data_start;
>> +	int data_len;
>> +
>> +	/* Last committed NDP for post-commit operations. */
>> +	struct usb_cdc_ncm_ndp16 *skb_ndp;
>> +
>> +	/* Non-committed NDP */
>> +	struct usb_cdc_ncm_ndp16 *ndp;
>>  };
>>
>>  static int huawei_cdc_ncm_manage_power(struct usbnet *usbnet_dev, int on)
>> @@ -53,6 +92,149 @@ static int huawei_cdc_ncm_manage_power(struct usbnet *usbnet_dev, int on)
>>  	return 0;
>>  }
>>
>> +/* huawei_ncm_mgmt: flexible TX NCM manager.
>> + *
>> + * Once a non-zero status value is rturned, current frame should be discarded
>> + * and operations restarted from scratch.
>> + */
>
> Is there any advantage in keeping this in a single function?
>
I did this choice in the light of the fact I think the tx_fixup function will 
become more complex than it is now, when aggregating frames.
I answer here your other message to make it more convenient to read: my 
intention for the tx_fixup function would be to:
- aggregate frames
- send them out when:
 	- a timer expires
 	OR
 	- we have enough data in the aggregate, and cannot add more.

This is something done in cdc_ncm.c for example.
But here I have a question: by reading the comment in file 
drivers/net/usb/rndis_host.c at line 572, there seem to be different opinions 
in this matter.
What to do ?

>> +int
>> +huawei_ncm_mgmt(struct usbnet *dev,
>> +		struct huawei_cdc_ncm_state *drvstate, struct sk_buff *skb_out, int mode) {
>> +	struct usb_cdc_ncm_nth16 *nth16 = (struct usb_cdc_ncm_nth16 *)skb_out->data;
>> +	struct cdc_ncm_ctx *ctx = drvstate->ctx;
>> +	struct usb_cdc_ncm_ndp16 *ndp16 = NULL;
>> +	int ret = -EINVAL;
>> +	u16 ndplen, index;
>> +
>> +	switch (mode) {
>> +	case NCM_INIT_FRAME:
>> +
>> +		/* Write a new NTH16 header */
>> +		nth16 = (struct usb_cdc_ncm_nth16 *)memset(skb_put(skb_out, sizeof(struct usb_cdc_ncm_nth16)), 0, sizeof(struct usb_cdc_ncm_nth16));
>> +		if (!nth16) {
>> +			ret = -EINVAL;
>> +			goto error;
>> +		}
>> +
>> +		/* NTH16 signature and header length are known a-priori. */
>> +		nth16->dwSignature = cpu_to_le32(USB_CDC_NCM_NTH16_SIGN);
>> +		nth16->wHeaderLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
>> +
>> +		/* TX sequence numbering */
>> +		nth16->wSequence = cpu_to_le16(ctx->tx_seq++);
>> +
>> +		/* Forget about previous SKB NDP */
>> +		drvstate->skb_ndp = NULL;
>
> This is probably better done after you know you cannot fail.
Sure. Thank you.
>
>> +
>> +		/* Allocate a new NDP */
>> +		ndp16 = kzalloc(ctx->max_ndp_size, GFP_NOIO);
>
> Where is this freed?
The intention wqas to free it in the NCM_COMMIT_NDP case.
Infact after allocating the pointer, I make a copy of it in the driver state 
(drvstate) variable, and get back to it later.
Is this wrong?
>
>> +		if (!ndp16)
>> +			return ret;
>> +
>> +		/* Prepare a new NDP to add data on subsequent calls. */
>> +		drvstate->ndp = memset(ndp16, 0, ctx->max_ndp_size);
>
> Either kzalloc() or memset(). Using both never makes sense.
>
True. Sorry - I knew that the "z" in kzalloc stood for ZERO and also looked at 
the code, but I forgot it at some point.

>> +
>> +		/* Initial NDP length */
>> +		ndp16->wLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_ndp16) + sizeof(struct usb_cdc_ncm_dpe16));
>> +
>> +		/* Frame signature: to be reworked in general. */
>> +			ndp16->dwSignature = cpu_to_le32(USB_CDC_NCM_NDP16_NOCRC_SIGN);
>> +
>> +			ret = 0;
>> +			break;
>> +
>> +	case NCM_UPDATE_NDP:
>> +
>> +		if (drvstate->skb_ndp) {
>> +			ndp16 = drvstate->skb_ndp;
>> +		} else {
>> +			ndp16 = drvstate->ndp;
>> +
>> +			/* Do we have enough space for the data? */
>> +			if (skb_out->len + ctx->max_ndp_size > ctx->tx_max)
>> +				goto error;
>> +		}
>> +
>> +		/* Calculate frame number within this NDP */
>> +		ndplen = le16_to_cpu(ndp16->wLength);
>> +		index = (ndplen - sizeof(struct usb_cdc_ncm_ndp16)) / sizeof(struct usb_cdc_ncm_dpe16) - 1;
>> +
>> +		if (index >= CDC_NCM_DPT_DATAGRAMS_MAX)
>> +			goto error;
>> +
>> +		/* tx_max shouldn't be exceeded after committing. */
>> +		if (ndplen + sizeof(struct usb_cdc_ncm_dpe16) > ctx->tx_max)
>> +				goto error;
>> +
>> +		/* Adding a DPT entry. */
>> +		ndp16->dpe16[index].wDatagramLength = cpu_to_le16(drvstate->data_len);
>> +		ndp16->dpe16[index].wDatagramIndex = cpu_to_le16(drvstate->data_start);
>> +		ndp16->wLength = cpu_to_le16(ndplen + sizeof(struct usb_cdc_ncm_dpe16));
>> +
>> +		ret = 0;
>> +		break;
>> +
>> +	case NCM_COMMIT_NDP:
>> +
>> +		if (drvstate->skb_ndp)
>> +			goto error;	/* Call this only once please. */
>> +
>> +		ndp16 = drvstate->ndp;
>> +
>> +		nth16->wNdpIndex = cpu_to_le16(skb_out->len);
>> +
>> +		/* "commit" NDP */
>> +		drvstate->skb_ndp = memcpy(skb_put(skb_out, ctx->max_ndp_size), ndp16, ctx->max_ndp_size);
>> +
>> +		kfree(ndp16);
>> +		ndp16 = NULL;
>> +		drvstate->ndp = NULL;
>> +
>> +	case NCM_FINALIZE_NTH:
>> +
>> +		/* Finalize NTH16 header, setting it's block length */
>> +		nth16->wBlockLength = cpu_to_le16(skb_out->len);
>> +
>> +		ret = 0;
>> +		break;
>> +	default:
>> +		break;
>> +	}
>> +
>> +error:
>
> The purpose of a label is kind of defeated by having a conditional after
> it.
>
The purpose here was to be sure to deallocate everything could needed to, even 
reaching the label from multiple places.
I'll look at it again now.
>> +	if (ret)
>> +		kfree(drvstate->ndp);
>> +	return ret;
>> +}
>
> 	Regards
> 		Oliver
>
>
>
Thank you very much Oliver.

Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Oliver Neukum]

On Thu, 2015-06-25 at 13:44 +0200, Enrico Mioso wrote:

> On Thu, 25 Jun 2015, Oliver Neukum wrote:

> > Is there any advantage in keeping this in a single function?
> >
> I did this choice in the light of the fact I think the tx_fixup function will 
> become more complex than it is now, when aggregating frames.

Yes, but that is a reason to split the helpers up not the opposite.

> I answer here your other message to make it more convenient to read: my 
> intention for the tx_fixup function would be to:
> - aggregate frames
> - send them out when:
>  	- a timer expires

How would you do that in tx_fixup()? If a timer is required then you
need a separate function.

>  	OR
>  	- we have enough data in the aggregate, and cannot add more.

Yes.

You need a third case:
	- the interface is taken down.

But in general the logic for that is already there. So can you explain
what additional goals you have?

> This is something done in cdc_ncm.c for example.
> But here I have a question: by reading the comment in file 
> drivers/net/usb/rndis_host.c at line 572, there seem to be different opinions 
> in this matter.

That is a very old comment written for much slower devices.
rndis_host doesn't get much love nowadays.

> What to do ?
> 
> >> +int
> >> +huawei_ncm_mgmt(struct usbnet *dev,
> >> +		struct huawei_cdc_ncm_state *drvstate, struct sk_buff *skb_out, int mode) {
> >> +	struct usb_cdc_ncm_nth16 *nth16 = (struct usb_cdc_ncm_nth16 *)skb_out->data;
> >> +	struct cdc_ncm_ctx *ctx = drvstate->ctx;
> >> +	struct usb_cdc_ncm_ndp16 *ndp16 = NULL;
> >> +	int ret = -EINVAL;
> >> +	u16 ndplen, index;
> >> +
> >> +	switch (mode) {
> >> +	case NCM_INIT_FRAME:
> >> +
> >> +		/* Write a new NTH16 header */
> >> +		nth16 = (struct usb_cdc_ncm_nth16 *)memset(skb_put(skb_out, sizeof(struct usb_cdc_ncm_nth16)), 0, sizeof(struct usb_cdc_ncm_nth16));
> >> +		if (!nth16) {
> >> +			ret = -EINVAL;
> >> +			goto error;
> >> +		}
> >> +
> >> +		/* NTH16 signature and header length are known a-priori. */
> >> +		nth16->dwSignature = cpu_to_le32(USB_CDC_NCM_NTH16_SIGN);
> >> +		nth16->wHeaderLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
> >> +
> >> +		/* TX sequence numbering */
> >> +		nth16->wSequence = cpu_to_le16(ctx->tx_seq++);
> >> +
> >> +		/* Forget about previous SKB NDP */
> >> +		drvstate->skb_ndp = NULL;
> >
> > This is probably better done after you know you cannot fail.
> Sure. Thank you.
> >
> >> +
> >> +		/* Allocate a new NDP */
> >> +		ndp16 = kzalloc(ctx->max_ndp_size, GFP_NOIO);
> >
> > Where is this freed?
> The intention wqas to free it in the NCM_COMMIT_NDP case.
> Infact after allocating the pointer, I make a copy of it in the driver state 
> (drvstate) variable, and get back to it later.
> Is this wrong?

Well, no, but it supposes a matched commit phase. Can you guarantee
that? I was under the oppression that in that phase you want to actually
give a frame over to the hardware.



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Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Enrico Mioso]

[-- Attachment #1: Type: text/plain, Size: 5430 bytes --]

Hi Oliver! And thank you again.

I like / recommend the usage of open messaging standards: my preferred XMPP ID
(JID) is: mrkiko@jit.si.

On Thu, 25 Jun 2015, Oliver Neukum wrote:

> Date: Thu, 25 Jun 2015 15:38:46
> From: Oliver Neukum <oneukum@suse.de>
> To: Enrico Mioso <mrkiko.rs@gmail.com>
> Cc: linux-usb@vger.kernel.org, netdev@vger.kernel.org
> Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
> 
> On Thu, 2015-06-25 at 13:44 +0200, Enrico Mioso wrote:
>
>> On Thu, 25 Jun 2015, Oliver Neukum wrote:
>
>>> Is there any advantage in keeping this in a single function?
>>>
>> I did this choice in the light of the fact I think the tx_fixup function will
>> become more complex than it is now, when aggregating frames.
>
> Yes, but that is a reason to split the helpers up not the opposite.
Right - I understood only now your observation.

the only reason to write the manager that way was that it shouldn't become very 
complex - it should simply do things to frames, helping out in building valid 
NCM packages.

>
>> I answer here your other message to make it more convenient to read: my
>> intention for the tx_fixup function would be to:
>> - aggregate frames
>> - send them out when:
>>  	- a timer expires
>
> How would you do that in tx_fixup()? If a timer is required then you
> need a separate function.
>
Sure. I meant: I will adapt it in case needed, and expectin the code to become 
a little bit more convoluted.
>>  	OR
>>  	- we have enough data in the aggregate, and cannot add more.
>
> Yes.
>
> You need a third case:
> 	- the interface is taken down.
>
> But in general the logic for that is already there. So can you explain
> what additional goals you have?
regarding the "timer logic" I saw it in cdc_ncm.c, but I should study it in 
more detail to understand it and implement it here where needed in case.
And sure, the "interface goes down" case is important: didn't think about it.
Thanks for the point.

the only other additional goal is to use the manager in such a way that NDP 
will be disposed after frames.

I think that this split between NCM management and tx_fixup makes things more 
flexible in general: this is the reason for re-writing it.

>> This is something done in cdc_ncm.c for example.
>> But here I have a question: by reading the comment in file
>> drivers/net/usb/rndis_host.c at line 572, there seem to be different opinions
>> in this matter.
>
> That is a very old comment written for much slower devices.
> rndis_host doesn't get much love nowadays.
Fine.
>
>> What to do ?
>>
>>>> +int
>>>> +huawei_ncm_mgmt(struct usbnet *dev,
>>>> +		struct huawei_cdc_ncm_state *drvstate, struct sk_buff *skb_out, int mode) {
>>>> +	struct usb_cdc_ncm_nth16 *nth16 = (struct usb_cdc_ncm_nth16 *)skb_out->data;
>>>> +	struct cdc_ncm_ctx *ctx = drvstate->ctx;
>>>> +	struct usb_cdc_ncm_ndp16 *ndp16 = NULL;
>>>> +	int ret = -EINVAL;
>>>> +	u16 ndplen, index;
>>>> +
>>>> +	switch (mode) {
>>>> +	case NCM_INIT_FRAME:
>>>> +
>>>> +		/* Write a new NTH16 header */
>>>> +		nth16 = (struct usb_cdc_ncm_nth16 *)memset(skb_put(skb_out, sizeof(struct usb_cdc_ncm_nth16)), 0, sizeof(struct usb_cdc_ncm_nth16));
>>>> +		if (!nth16) {
>>>> +			ret = -EINVAL;
>>>> +			goto error;
>>>> +		}
>>>> +
>>>> +		/* NTH16 signature and header length are known a-priori. */
>>>> +		nth16->dwSignature = cpu_to_le32(USB_CDC_NCM_NTH16_SIGN);
>>>> +		nth16->wHeaderLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_nth16));
>>>> +
>>>> +		/* TX sequence numbering */
>>>> +		nth16->wSequence = cpu_to_le16(ctx->tx_seq++);
>>>> +
>>>> +		/* Forget about previous SKB NDP */
>>>> +		drvstate->skb_ndp = NULL;
>>>
>>> This is probably better done after you know you cannot fail.
>> Sure. Thank you.
>>>
>>>> +
>>>> +		/* Allocate a new NDP */
>>>> +		ndp16 = kzalloc(ctx->max_ndp_size, GFP_NOIO);
>>>
>>> Where is this freed?
>> The intention wqas to free it in the NCM_COMMIT_NDP case.
>> Infact after allocating the pointer, I make a copy of it in the driver state
>> (drvstate) variable, and get back to it later.
>> Is this wrong?
>
> Well, no, but it supposes a matched commit phase. Can you guarantee
> that? I was under the oppression that in that phase you want to actually
> give a frame over to the hardware.
No. When Italk about committing, I think about "writing things to out skb".
another reason why i found confortable writing the code this way was to 
maintain a kind of statefullness in a more "clean" way.
But I understand this is kind of agruable, and I can if needed break it up as 
desired.

Regarding the commit phase - I am not sure I understand your comment, sorry
about that.
However, my intention would be to allow the caller to do calls in sequences 
like:
- init frame
- ncm update
- ncm update
- ncm update
...
- ncm update
- ncm commit

(to work in "huawei" mode)

OR

- ncm init frame
- ncm commit
- ncm update
- ncm update
- ncm update
- ncm update
- finalize nth

(to work in "cdc_ncm.c"-mode)..


But to prevent usbnet from submittinx RX'd packets, I should be doing something 
nasty here. And unfortunately don't understand why.
Infact, this problem manifested itself even more aggressively when I kzallocìed 
in the _bind() function and kfreed in _unbind. I searched around this "kevent 2 
may have been dropped" (rx memory exhaustion) problem, but without finding 
significant hints.
Any idea would be welcome.
>
>
>

Thank you Oliver,
everyone.
Enrico

Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Oliver Neukum]

On Thu, 2015-06-25 at 17:19 +0200, Enrico Mioso wrote:
> Hi Oliver! And thank you again.
> 
> I like / recommend the usage of open messaging standards: my preferred XMPP ID
> (JID) is: mrkiko-aHS423dKhWw@public.gmane.org
> 
> On Thu, 25 Jun 2015, Oliver Neukum wrote:
> 
> > Date: Thu, 25 Jun 2015 15:38:46
> > From: Oliver Neukum <oneukum-l3A5Bk7waGM@public.gmane.org>
> > To: Enrico Mioso <mrkiko.rs-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > Cc: linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> > Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
> > 
> > On Thu, 2015-06-25 at 13:44 +0200, Enrico Mioso wrote:
> >
> >> On Thu, 25 Jun 2015, Oliver Neukum wrote:
> >
> >>> Is there any advantage in keeping this in a single function?
> >>>
> >> I did this choice in the light of the fact I think the tx_fixup function will
> >> become more complex than it is now, when aggregating frames.
> >
> > Yes, but that is a reason to split the helpers up not the opposite.
> Right - I understood only now your observation.
> 
> the only reason to write the manager that way was that it shouldn't become very 
> complex - it should simply do things to frames, helping out in building valid 
> NCM packages.
> 
> >
> >> I answer here your other message to make it more convenient to read: my
> >> intention for the tx_fixup function would be to:
> >> - aggregate frames
> >> - send them out when:
> >>  	- a timer expires
> >
> > How would you do that in tx_fixup()? If a timer is required then you
> > need a separate function.
> >
> Sure. I meant: I will adapt it in case needed, and expectin the code to become 
> a little bit more convoluted.

You cannot become any more convoluted even if you try.

> >>  	OR
> >>  	- we have enough data in the aggregate, and cannot add more.
> >
> > Yes.
> >
> > You need a third case:
> > 	- the interface is taken down.
> >
> > But in general the logic for that is already there. So can you explain
> > what additional goals you have?
> regarding the "timer logic" I saw it in cdc_ncm.c, but I should study it in 
> more detail to understand it and implement it here where needed in case.

It is involved. Basically a timer for transmission creates locking
issues. cdc-ncm uses an hrtimer which calls a bottom half which
calls xmit with a NULL skb.

        /* if there is a remaining skb, it gets priority */
        if (skb != NULL) {
                swap(skb, ctx->tx_rem_skb);
                swap(sign, ctx->tx_rem_sign);
        } else {
                ready2send = 1;
        }

The else branch here is the timer triggering.
The actual transmission is done in usbnet if cdc_ncm_fill_tx_frame()
returns an skb.

I doubt you can can come up with anything more convoluted
but it simplifies locking.

> > Well, no, but it supposes a matched commit phase. Can you guarantee
> > that? I was under the oppression that in that phase you want to actually
> > give a frame over to the hardware.
> No. When Italk about committing, I think about "writing things to out skb".
> another reason why i found confortable writing the code this way was to 
> maintain a kind of statefullness in a more "clean" way.
> But I understand this is kind of agruable, and I can if needed break it up as 
> desired.
> 
> Regarding the commit phase - I am not sure I understand your comment, sorry
> about that.
> However, my intention would be to allow the caller to do calls in sequences 
> like:
> - init frame
> - ncm update
> - ncm update
> - ncm update
> ...
> - ncm update
> - ncm commit
> 
> (to work in "huawei" mode)
> 
> OR
> 
> - ncm init frame
> - ncm commit
> - ncm update
> - ncm update
> - ncm update
> - ncm update
> - finalize nth
> 
> (to work in "cdc_ncm.c"-mode)..

Sounds like a plan.

> But to prevent usbnet from submittinx RX'd packets, I should be doing something 
> nasty here. And unfortunately don't understand why.

        // some devices want funky USB-level framing, for
        // win32 driver (usually) and/or hardware quirks
        if (info->tx_fixup) {
                skb = info->tx_fixup (dev, skb, GFP_ATOMIC);
                if (!skb) {
                        /* packet collected; minidriver waiting for more
*/
                        if (info->flags & FLAG_MULTI_PACKET)
                                goto not_drop;

So you just return NULL if you are ready to queue more. But you
need the FLAG_MULTI_PACKET flag.

	Regards
		Oliver


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Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Enrico Mioso]

Hi Oliver!
I wish sincerely to thank you again for your time and patience.

On Fri, 26 Jun 2015, Oliver Neukum wrote:

> Date: Fri, 26 Jun 2015 10:14:02
> From: Oliver Neukum <oneukum@suse.com>
> To: Enrico Mioso <mrkiko.rs@gmail.com>
> Cc: linux-usb@vger.kernel.org, netdev@vger.kernel.org
> Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
> 
> On Thu, 2015-06-25 at 17:19 +0200, Enrico Mioso wrote:
>> Hi Oliver! And thank you again.
>>
>> I like / recommend the usage of open messaging standards: my preferred XMPP ID
>> (JID) is: mrkiko@jit.si.
>>
>> On Thu, 25 Jun 2015, Oliver Neukum wrote:
>>
>>> Date: Thu, 25 Jun 2015 15:38:46
>>> From: Oliver Neukum <oneukum@suse.de>
>>> To: Enrico Mioso <mrkiko.rs@gmail.com>
>>> Cc: linux-usb@vger.kernel.org, netdev@vger.kernel.org
>>> Subject: Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack
>>>
>>> On Thu, 2015-06-25 at 13:44 +0200, Enrico Mioso wrote:
>>>
>>>> On Thu, 25 Jun 2015, Oliver Neukum wrote:
>>>
>>>>> Is there any advantage in keeping this in a single function?
>>>>>
>>>> I did this choice in the light of the fact I think the tx_fixup function will
>>>> become more complex than it is now, when aggregating frames.
>>>
>>> Yes, but that is a reason to split the helpers up not the opposite.
>> Right - I understood only now your observation.
>>
>> the only reason to write the manager that way was that it shouldn't become very
>> complex - it should simply do things to frames, helping out in building valid
>> NCM packages.
>>
>>>
>>>> I answer here your other message to make it more convenient to read: my
>>>> intention for the tx_fixup function would be to:
>>>> - aggregate frames
>>>> - send them out when:
>>>>  	- a timer expires
>>>
>>> How would you do that in tx_fixup()? If a timer is required then you
>>> need a separate function.
>>>
>> Sure. I meant: I will adapt it in case needed, and expectin the code to become
>> a little bit more convoluted.
>
> You cannot become any more convoluted even if you try.
>
>>>>  	OR
>>>>  	- we have enough data in the aggregate, and cannot add more.
>>>
>>> Yes.
>>>
>>> You need a third case:
>>> 	- the interface is taken down.
>>>
>>> But in general the logic for that is already there. So can you explain
>>> what additional goals you have?
>> regarding the "timer logic" I saw it in cdc_ncm.c, but I should study it in
>> more detail to understand it and implement it here where needed in case.
>
> It is involved. Basically a timer for transmission creates locking
> issues. cdc-ncm uses an hrtimer which calls a bottom half which
> calls xmit with a NULL skb.
>
>        /* if there is a remaining skb, it gets priority */
>        if (skb != NULL) {
>                swap(skb, ctx->tx_rem_skb);
>                swap(sign, ctx->tx_rem_sign);
>        } else {
>                ready2send = 1;
>        }
>
> The else branch here is the timer triggering.
> The actual transmission is done in usbnet if cdc_ncm_fill_tx_frame()
> returns an skb.
>
> I doubt you can can come up with anything more convoluted
> but it simplifies locking.
>
>>> Well, no, but it supposes a matched commit phase. Can you guarantee
>>> that? I was under the oppression that in that phase you want to actually
>>> give a frame over to the hardware.
>> No. When Italk about committing, I think about "writing things to out skb".
>> another reason why i found confortable writing the code this way was to
>> maintain a kind of statefullness in a more "clean" way.
>> But I understand this is kind of agruable, and I can if needed break it up as
>> desired.
>>
>> Regarding the commit phase - I am not sure I understand your comment, sorry
>> about that.
>> However, my intention would be to allow the caller to do calls in sequences
>> like:
>> - init frame
>> - ncm update
>> - ncm update
>> - ncm update
>> ...
>> - ncm update
>> - ncm commit
>>
>> (to work in "huawei" mode)
>>
>> OR
>>
>> - ncm init frame
>> - ncm commit
>> - ncm update
>> - ncm update
>> - ncm update
>> - ncm update
>> - finalize nth
>>
>> (to work in "cdc_ncm.c"-mode)..
>
> Sounds like a plan.
>
>> But to prevent usbnet from submittinx RX'd packets, I should be doing something
>> nasty here. And unfortunately don't understand why.
>
>        // some devices want funky USB-level framing, for
>        // win32 driver (usually) and/or hardware quirks
>        if (info->tx_fixup) {
>                skb = info->tx_fixup (dev, skb, GFP_ATOMIC);
>                if (!skb) {
>                        /* packet collected; minidriver waiting for more
> */
>                        if (info->flags & FLAG_MULTI_PACKET)
>                                goto not_drop;
>
> So you just return NULL if you are ready to queue more. But you
> need the FLAG_MULTI_PACKET flag.
>
Unfortuantely I might have not explained myself better.
I should thank you for this illumination on the timer part: since I know I'll need this.
But what's stopping me right now is actually the RX, not the TX part.
Sure, the RX function I am using comes from cdc_ncm.c and works fine: unfortunately, usbnet will not call it.
Infact, my dmesg ends up FULL of 
"kevent 2 may have been dropped" messages.
And looking around I discovered I end up triggering a memory check in usbnet.c, 
at line 475

 	skb = __netdev_alloc_skb_ip_align(dev->net, size, flags);
 	if (!skb) { /* triggered */
 		netif_dbg(dev, rx_err, dev->net, "no rx skb\n");
 		usbnet_defer_kevent (dev, EVENT_RX_MEMORY);
 		usb_free_urb (urb);
 		return -ENOMEM;
 	}

And genuinely, I can't understand why.
To test what I was doing wrong, I started with the stock huawei_cdc_ncm.c that 
works fine.
then I started allocating the temporary NDP in the bind function: and the 
problem started triggering, so I can't RX.
Allocating and deallocating the temporary NDP as-neede as happens now, triggers 
the problem inevitably after some packets: ping works for a while.

I was investigating on calls to obtain "private memory" as it happens in the 
hso.c driver and others, but wanted some feedback.

What happens then is I get a worker thread using all the CPU and ksoftirqs/0 
going mad.
Googling around resulted mainly in people complaining about this same problem 
with the drivers/net/usb/smsc95xx.c driver, used in the Raspberry PI for the 
Ethernet card.

I imagine in my case what's doing wrong could be terrible but I am not abe to 
tell right now.
I tried thinking how to avoid allocating the temporary NDP somehow: without a 
solution. And nowI would like to understand what's going wrong even for my 
personal kwoledge.

> 	Regards
> 		Oliver
>
>
>

Thank you again, and have a good weekend.
Enrico

Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Enrico Mioso]

Ok, for now I should let go of this - might be it was a little bit too much for 
the time constaints I am having.
But thank you for your effort Oliver.
Anyway, trying to write this new TX engine helped me in understand better 
things and conceive the patch I sent you affecting cdc_ncm.c, which triggers 
some OOPSes but not in a qemu vm, so I can't read them actually.

Any hint on my code is always apreciated, regardless.
Enrico
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Re: [PATCH RFC] 2/2 huawei_cdc_ncm: introduce new TX ncm stack

[Oliver Neukum]

On Tue, 2015-06-23 at 00:32 +0200, Enrico Mioso wrote:

> +/* XXX rewrite, not multipacket */

Can you explain what you want to do here?
> +struct sk_buff *
> +huawei_ncm_tx_fixup(struct usbnet *dev, struct sk_buff *skb_in, gfp_t flags) {
> +	struct huawei_cdc_ncm_state *drvstate = (void *)&dev->data;
> +	struct cdc_ncm_ctx *ctx = drvstate->ctx;
> +	struct sk_buff *skb_out;
> +	int status;
> +
> +	skb_out = alloc_skb(ctx->tx_max, GFP_ATOMIC);

You must test this for NULL

	Regards
		Oliver



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