linux-kernel - Re: [PATCH 11/30] usb: dwc2: gadget: Avoid pointless read of EP control register

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Date:   Fri, 3 Jul 2020 07:38:16 +0000
From:   Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Lee Jones <lee.jones@...aro.org>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Ben Dooks <ben@...tec.co.uk>
Subject: Re: [PATCH 11/30] usb: dwc2: gadget: Avoid pointless read of EP
 control register

Hi,

On 7/3/2020 11:29 AM, Greg KH wrote:
> On Thu, Jul 02, 2020 at 03:46:06PM +0100, Lee Jones wrote:
>> Commit ec1f9d9f01384 ("usb: dwc2: gadget: parity fix in isochronous mode") moved
>> these checks to dwc2_hsotg_change_ep_iso_parity() back in 2015.  The assigned
>> value hasn't been read back since.  Let's remove the unnecessary H/W read.
>>
>> Fixes the following W=1 warning:
>>
>>   drivers/usb/dwc2/gadget.c: In function ‘dwc2_hsotg_epint’:
>>   drivers/usb/dwc2/gadget.c:2981:6: warning: variable ‘ctrl’ set but not used [-Wunused-but-set-variable]
>>   2981 | u32 ctrl;
>>   | ^~~~
>>
>> Cc: Minas Harutyunyan <hminas@...opsys.com>
>> Cc: Ben Dooks <ben@...tec.co.uk>
>> Signed-off-by: Lee Jones <lee.jones@...aro.org>
>> ---
>>   drivers/usb/dwc2/gadget.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
>> index 116e6175c7a48..fa07e3fcb8841 100644
>> --- a/drivers/usb/dwc2/gadget.c
>> +++ b/drivers/usb/dwc2/gadget.c
>> @@ -2975,10 +2975,8 @@ static void dwc2_hsotg_epint(struct dwc2_hsotg *hsotg, unsigned int idx,
>>   	u32 epctl_reg = dir_in ? DIEPCTL(idx) : DOEPCTL(idx);
>>   	u32 epsiz_reg = dir_in ? DIEPTSIZ(idx) : DOEPTSIZ(idx);
>>   	u32 ints;
>> -	u32 ctrl;
>>   
>>   	ints = dwc2_gadget_read_ep_interrupts(hsotg, idx, dir_in);
>> -	ctrl = dwc2_readl(hsotg, epctl_reg);
> 
> As you know, lots of hardware requires reads to happen to do things, so
> are you sure it is safe to remove this read call?
> 

Greg, yes, it's Ok to remove this unnecessary read which remained from 
previous implementations.

Lee, please add "Fixes:" tag and resubmit v2.

Thanks,
Minas


> thanks,
> 
> greg k-h
>