linux-kernel - Re: [PATCH 1/4] Staging: rtl8192e: Remove variable bFirstSeg

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Date:   Mon, 11 Dec 2023 20:22:12 +0100
From:   Philipp Hortmann <philipp.g.hortmann@...il.com>
To:     Dan Carpenter <dan.carpenter@...aro.org>,
        Tree Davies <tdavies@...kphysics.net>
Cc:     gregkh@...uxfoundation.org, anjan@...i.ca,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] Staging: rtl8192e: Remove variable bFirstSeg

On 12/11/23 09:37, Dan Carpenter wrote:
> On Sun, Dec 10, 2023 at 11:37:02AM -0800, Tree Davies wrote:
>> Remove variable bFirstSeg as it is defined but never used.
>>
>> Signed-off-by: Tree Davies <tdavies@...kphysics.net>
>> ---
>>   drivers/staging/rtl8192e/rtllib.h | 1 -
>>   1 file changed, 1 deletion(-)
>>
>> diff --git a/drivers/staging/rtl8192e/rtllib.h b/drivers/staging/rtl8192e/rtllib.h
>> index 0a8c44e497f5..c0a24826cd3b 100644
>> --- a/drivers/staging/rtl8192e/rtllib.h
>> +++ b/drivers/staging/rtl8192e/rtllib.h
>> @@ -103,7 +103,6 @@ struct cb_desc {
>>   	/* Tx Desc Related flags (8-9) */
>>   	u8 bLastIniPkt:1;
>>   	u8 bCmdOrInit:1;
>> -	u8 bFirstSeg:1;
>>   	u8 bLastSeg:1;
>>   	u8 bEncrypt:1;
>>   	u8 tx_dis_rate_fallback:1;
> 
> I don't think you can remove these.  They're part of the protocol for
> talking to the firmware.
> 
> regards,
> dan carpenter
> 

Hi Dan,

thanks for your response.

struct cb_desc is used in conjunction with this line:
struct cb_desc *tcb_desc = (struct cb_desc *)(skb->cb + 8);
from skbuff.h:
	/*
	 * This is the control buffer. It is free to use for every
	 * layer. Please put your private variables there. If you
	 * want to keep them across layers you have to do a skb_clone()
	 * first. This is owned by whoever has the skb queued ATM.
	 */
	char			cb[48] __aligned(8);

I think it has to do with the sku buffer and can be changed.

Here a test:
kernel@...rix-ESPRIMO-P710:~/Documents/git/kernels/staging$ git diff
diff --git a/drivers/staging/rtl8192e/rtllib.h 
b/drivers/staging/rtl8192e/rtllib.h
index cc9070f39004..f29efc605ba9 100644
--- a/drivers/staging/rtl8192e/rtllib.h
+++ b/drivers/staging/rtl8192e/rtllib.h
@@ -100,6 +100,7 @@ static inline void *netdev_priv_rsl(struct 
net_device *dev)
  /* defined for skb cb field */
  /* At most 28 byte */
  struct cb_desc {
+       u8 ph_temp[7];
         /* Tx Desc Related flags (8-9) */
         u8 bLastIniPkt:1;
         u8 bCmdOrInit:1;
diff --git a/drivers/staging/rtl8192e/rtllib_softmac.c 
b/drivers/staging/rtl8192e/rtllib_softmac.c
index ee527ba5d1a8..93292fc3faaf 100644
--- a/drivers/staging/rtl8192e/rtllib_softmac.c
+++ b/drivers/staging/rtl8192e/rtllib_softmac.c
@@ -189,6 +189,9 @@ inline void softmac_mgmt_xmit(struct sk_buff *skb, 
struct rtllib_device *ieee)
         struct cb_desc *tcb_desc = (struct cb_desc *)(skb->cb + 8);

         spin_lock_irqsave(&ieee->lock, flags);
+       printk("Setting tcb_desc !!!\n");
+       tcb_desc->ph_temp[0] = 0xAA;
+       tcb_desc->ph_temp[6] = 0xAA;

         /* called with 2nd param 0, no mgmt lock required */
         rtllib_sta_wakeup(ieee, 0);

Here the log:
[ 9024.740612] rtl819xE 0000:03:00.0: Adapter(8192 PCI-E) is found - 
DeviceID=8192
[ 9025.773658] Setting tcb_desc !!!
[ 9025.773783] Setting tcb_desc !!!
[ 9025.797635] Setting tcb_desc !!!
[ 9025.797701] Setting tcb_desc !!!
[ 9025.849687] Setting tcb_desc !!!
[ 9025.849743] Setting tcb_desc !!!
[ 9025.977703] Setting tcb_desc !!!
[ 9025.977740] Setting tcb_desc !!!
[ 9026.105693] Setting tcb_desc !!!

Performance as expected OK.

Please reconsider your decision?

Thanks

Bye Philipp