linux-kernel - Re: [PATCH 4/5] staging: rtl8192e: Remove unused local variable irq

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Date:   Fri, 7 Apr 2023 10:08:50 +0200
From:   Philipp Hortmann <philipp.g.hortmann@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] staging: rtl8192e: Remove unused local variable
 irq_line

On 4/6/23 22:06, Greg Kroah-Hartman wrote:
> On Wed, Apr 05, 2023 at 11:48:20PM +0200, Philipp Hortmann wrote:
>> Remove unused local variable irq_line.
>>
>> Signed-off-by: Philipp Hortmann <philipp.g.hortmann@...il.com>
>> ---
>>   drivers/staging/rtl8192e/rtl8192e/rtl_pci.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/staging/rtl8192e/rtl8192e/rtl_pci.c b/drivers/staging/rtl8192e/rtl8192e/rtl_pci.c
>> index 0bc3e013001e..1c3ccd2aabc3 100644
>> --- a/drivers/staging/rtl8192e/rtl8192e/rtl_pci.c
>> +++ b/drivers/staging/rtl8192e/rtl8192e/rtl_pci.c
>> @@ -33,11 +33,9 @@ bool rtl92e_check_adapter(struct pci_dev *pdev, struct net_device *dev)
>>   	struct r8192_priv *priv = (struct r8192_priv *)rtllib_priv(dev);
>>   	u16 device_id;
>>   	u8  revision_id;
>> -	u16 irq_line;
>>   
>>   	device_id = pdev->device;
>>   	revision_id = pdev->revision;
>> -	pci_read_config_word(pdev, 0x3C, &irq_line);
> 
> As was pointed out, that might not be "unused".
> 
> When doing a PCI write, the only way to know it has completed is to
> issue a read.  Are you sure this isn't a read that is flushing out a
> pending write?  Look at who calls this function and verify that this
> read really is safe to remove and then document that really really well
> in the changelog text when doing so.
> 
> Be careful about removing seemingly-unused PCI read/writes, they often
> times are actually needed.
> 
> thanks,
> 
> greg k-h

Hi,

The first function that is called of the driver is: _rtl92e_pci_probe().
66 Lines later the function rtl92e_check_adapter() is called. The line
pci_read_config_word() is the 10th line of this function.

No other pci function before in function rtl92e_check_adapter().

The following functions are used in the probe function before the
rtl92e_check_adapter():

pci_enable_device()		Does not require a pci read.
pci_set_master()		Does not require a pci read.
dma_set_mask()			Does not require a pci read.
alloc_rtllib()			Does not require a pci read.
pci_set_drvdata()		Does not require a pci read.
SET_NETDEV_DEV()		Does not require a pci read.
rtllib_priv()			Does not require a pci read.
pci_resource_start()		Does not require a pci read.
pci_resource_len()		Does not require a pci read.
pci_resource_flags()		Does not require a pci read.
request_mem_region()		Does not require a pci read.
ioremap()			Does not require a pci read.
pci_resource_len()		Does not require a pci read.
pci_read_config_byte()		Which is deleted in this
				patch series. So Gregs hint is
  				applicable for this patch as well.

I am going to issue a v2.

Thanks for your support.

Bye Philipp